Horrible Horrible feeling. Can come in many forms, diferent thoughts and symptoms.
Just remember whatever you are going trough, many been there before and came back, but also many didn't, thats why if you notice you might be depressed you should seek professional help. If you had it before, definitly do it, you have the advantage of reconising it early.
Exercise helps alot, stay of sugar, cold showers(raise testosterone levels), eat on time, sleep on time.