You know those feelings of general discontent, sadness, and hopelessness? If you have them, don't ignore them. They could be signs of something much worse, like depression.

While I'm no shrink, I have lots of experience with clients (and a close family member) who struggle with it, and I have learned to identify the signs (which I will cover below).

Entrepreneurs are certainly not exempt. A study by Dr. Michael Freeman, a clinical professor at UC San Francisco, revealed that nearly half suffered from anxiety and depression.

Before I detail the obvious signs, take this in from entrepreneur Brad Feld, co-founder of Foundry Group, who wrote this Inc. article describing his struggles with depression.

I've struggled with serious bouts of depression three times in my life. I'm not talking about a series of miserable days or struggling through the pressure and stress of a failing company. I'm talking about months of feeling emotionally drained.

My latest episode began in January and lifted only in May after months of feeling completely exhausted. In the fall, I was logging 80-plus-hour weeks on a regular basis, traveling most of the time, trying to recover from a bike accident without taking any time off, and sleeping poorly. I wasn't running regularly, which is usually how I get time alone. And in an alarming health scare in October, I wound up in the hospital for surgery to remove a kidney stone.

By January, I had slipped into a deep depression. The joy went out of everything. I spent February through April prying myself out of bed, going through the motions at work, and just waiting to crawl back into bed again.

This is what depression feels like. I'm lucky in that I have an incredible wife, friends, and colleagues who gave me space and simply listened to me, without judgment. My depression eventually lifted, as it has twice before in my life.

The worst part about depression is that it is often linked to high rates of suicide -- the highest cause of death for people aged 15-49 in the developed world.

Even Tim Ferris, of all people, blogged candidly about his battle with depression and how he almost killed himself while a student at Princeton.

Let's talk about the signs.

1. You feel fatigue and don't sleep (or sleep too much).

Depression strips you of your energy and makes you feel lethargic. You stop doing things you enjoy because you feel exhausted, and begin sleeping excessively, or not sleeping at all (insomnia).

2. Your emotions are all over the place.

One moment, you're feeling irritable and going off on someone in a full display of anger. The next, you're crying. Depression can swing your moods uncontrollably.

3. Your topics of conversation have turned morbid.

Suicides rarely come without the symptoms that show up beforehand. Depressed people will often talk about it. If you're in the company of a good friend who has flipped the morbid switch to "on" and is now talking about death and dying, stay close and monitor him. He may be on the doorstep of a suicide attempt.

4. Your outlook on life has done a 180.

Having a hopeless or helpless outlook on life is the most common symptom of depression. Associated feelings of worthlessness, self-hate, or inappropriate guilt may be riding shotgun. You vocalize thoughts like "It's all my fault," and "What's the point?"

5. You've lost interest in the things you enjoy.

Depression can rob you of the things you love, making you withdrawing from the very activities you once looked forward to -- sports, socializing with friends, hobbies, etc.

What to do.

If depression has crept in, don't despair. With professional help and a strong support system of loving family and friends, you can overcome it. Here's what you can do:

  • Please sleep. Don't set the alarm. Just sleep until you wake up.
  • Do not isolate yourself--find community and support.
  • Don't internalize your feelings. Be totally present with them.
  • Express gratitude. Both Ferriss and Shawn Achor suggest taking one-to-two minutes every day to call or email someone and express gratitude about something.

  • Journal your feelings daily to help release those negative emotions.

  • Lean on your faith, or something greater than you.
  • Rediscover the activities and hobbies that bring you peace, joy, and vitality.
  • Exercise daily. Fifteen minutes of cardio is all it takes.
  • Practice mindfulness.

And if you are at that really bad place, where no article in the world can help you, then call this number now: 1 (800) 273-8255. It's the National Suicide Prevention Lifeline (website and live chat here). It's available 24 hours a day, seven days a week, in both English and Spanish. If you're outside of the U.S., please click here for a list of international hotlines.