Feeling lethargic only brings more negativity, one can only have so much negativity before it consumes every part of your day and you'll just become sick and tired of being sick and tired.
Whenever I use to feel happy or content in anyway, I triggered off some thoughts that bring a lot of sudden negativity. Like a freind who put a smile on my face but suddenly I remembered how he nearly screwed me over 2 years ago or said something offensive etc
The best thing is to try to be in control of your emotions. If you are upset or pissed off, allow those thoughts to pass you, have a mental discussion with yourself and come to a sensible conclusion about it then move on. And it's a learning curve. Moving on is the hardest skill to have as a person. Chances are you will visit your problems every so often and maybe even create new problems to avoid that visit. The World is a short stay. Don't let anyone or anything steal your thunder. Do what makes you happy because a whole load of people out there wish they pursued that instead of whatever else they did.
Hope that helps
@Barni