Are you suffering from the blues or clinical depression? Experts reveal the symptoms of depression and when you should see a doctor for treatment.

When its more than just the blues

Feeling down in the dumps every so often is a normal part of life. But when you're gripped by an unrelenting sadness or hopelessness that keeps you from going about your usual routine, it's time to pay attention: it's the hallmark sign of clinical depression, and an estimated 7% of adults will experience it, according to the National Institute of Mental Health. Even with this telltale sign in place, it's tough for a depressed person to know if she really has the disease.

"Almost all of the symptoms of depression on their own are experienced by everyone at one time or another," explains Jennifer Payne, MD, director of the Women's Mood Disorders Center at Johns Hopkins University in Baltimore. If you've been dealing with four or more of the following symptoms every day for two weeks, and they've impaired the way you usually function (for example, prevented you from working, being a responsible parent, or seeing friends), it's time to check in with your doctor.

You're eating more (or less) than usual

Depression leaves you withdrawn and checked out, and that can manifest as a loss of appetite. "If your brain is preoccupied with negative thoughts, you may forget to eat or lose interest in cooking or preparing meals," says Yvonne Thomas, PhD, Los Angeles-based psychologist specializing in depression and self-esteem.

On the other hand, sometimes the disease kicks in the opposite effect, making you hungry and driving you to overeat. "The mix of emotions that tend to accompany depression—sadness, pessimism about the future, and low self-esteem—can compel you to try to soothe your feelings with food binges," says Thomas.

You're sleeping too much or too little

Some people with depression find themselves snoozing under the covers more; the disengagement and dip in energy make you tired all the time, says Thomas. "Sleeping more is also a way depressed people escape from their sadness; it becomes a refuge," she adds.

Others with depression experience restless or interrupted sleep or even insomnia—they're too wired by obsessive thoughts or ruminations to wind down and score the seven to eight hours per night most adults need.

Thing is, not only can sleep changes be a tipoff to the disease, but they also make it worse. When you're not getting the proper amount of shuteye, your body's internal clock gets out of sync, and you're even more tired and unfocused...and less able to cope.

Small things agitate you

It's a sneaky sign few people recognize: depression can show up as heightened irritability, says Jennifer Wolkin, PhD, clinical assistant professor in the department of psychiatry and anesthesiology at New York University's Joan H. Tisch Center for Women's Health. You might feel cranky and grumpy; little things that normally wouldn't register set you off and leave you snapping at friends and coworkers.

Part of the prickliness may be the way depression exacerbates normal hormonal swings. But it could also be triggered by the weight of so many heavy emotions. "When people are in physical pain, they often get angry and irritated easily, and it's the same with psychological pain—you don't feel good or like your usual self, and that saps your patience and puts you more on edge," says Thomas.

You can't concentrate or focus

Forgetting work deadlines or when to pick up your kids from a playdate? Feel like your mind resembles an out-of-focus photo, and the fuzziness has made a dent in the way you weigh choices and make decisions?

That's your brain on depression. Being preoccupied with thoughts of sadness and emptiness can plunge you into a head fog that affects your job, memory, and decision-making skills, says Wolkin.

In turn, that unfocused thinking can lead you to make poor choices or take on unhealthy, risky behavior.

You don't enjoy the things that once made you happy

You used to hit happy hour with your favorite group of coworkers, but for the last few weeks, you've been ducking out. Or you always looked forward to your nightly run, but these days, you can't muster the interest.

Not taking part in things you once enjoyed because they no longer give you pleasure is a telltale sign of depression. "A person who is simply blue might skip a few outings, then get back in the swing of things," says Wolkin.

"But depression makes you apathetic about activities and hobbies that once gave you joy, and that makes you isolate yourself." It sets up that vicious cycle: depression robs you of your ability to derive pleasure from experiences, so you stop doing the very things that could brighten your mood.

You feel down on yourself and worthless

If you're constantly putting yourself down, or you feel worthless or inconsequential, something is up. "Repetitive thoughts along the lines of 'I'm not good enough' or 'I don't matter' are dangerous because they can fuel self-harming behavior," says Wolkin.

When you think this way, you tend to find ways to verify the negativity, and that in turn makes you more depressed and more at risk. Extreme guilt for things you are not solely responsible for—for example, a bad breakup or sudden job loss—also bashes your self-esteem and is a tip-off to depression, says Dr. Payne.

You're preoccupied with thoughts of death

Persistent thoughts about ending your life, wondering how friends and family would feel if you went and did it, pondering different ways to carry out the act, and even general thoughts about death are all strong indicators that it's time to reach out for professional help, says Wolkin.

"Because these thoughts pose such a direct threat to your life, it's important to seek help if you experience them daily or almost every day for two weeks, even if you don't recognize any other symptoms of depression in yourself," she says.

You're panicky and anxious

Overwhelming feelings of fear are usually thought to signify an anxiety disorder. And while that's often true, they can also be a clue to depression. "Anxious feelings often coincide with depression, and some depressed people have panic attacks," says Dr. Payne.

Anxiety is more than just the normal apprehension most of us feel when we're challenged; it's a constant feeling of panic and obsessive thoughts that often show up in physical symptoms such as rapid heartbeat, excessive perspiration, and sleep problems.

The tricky thing is, even though anxiety can signal depression, it's possible that a person with depression also has an anxiety disorder as well. If you feel overwhelming anxiety, consider it another crucial reason to seek help from your doc.

Your energy level has hit the wall

Depression-related lethargy may be simply the consequence of not eating enough or sleeping too much. But it's also the result of having a black cloud of sadness or hopelessness over you all the time.

Dealing with chronic emotional pain is an energy suck, and it makes you too dragged and tired to tackle routine tasks, not to mention work and family responsibilities. "You feel overwhelmed by day to day life; even getting out of bed and taking a shower becomes exhausting," says Wolkin. When you're always tired and that fatigue impairs your life, it's time to seek help.

You're dealing with unexplained aches and pains

"Emotional pain from depression that you aren't getting help for can be channeled throughout your body and show up as physical ailments, like headaches, stomach problems, neck and back pain, even nausea," says Thomas. "I see this with many of my patients; they're holding so much sadness and distress inside; these feelings end up playing out in other ways."

Not every cramp or twinge is a symptom of depression, of course. But if you're suffering from a chronic ailment you can't attribute to another cause that isn't clearing up on its own, "see a doctor to get it checked out, but also consider it a possible sign of depression too," says Thomas.