I have to run out now, but I have a lot more to tell you. Exercise is key, whenever I am in a bad mood I realize that it has been too long since I've exercised. Your body will actually generate new neurons while you are exercising and your brain will release endorphins and other neurotransmitters that increase mood. I know it seems hard to get there if you haven't been in a while, but for a longterm goal and short term boosts of energy, definitely do it. You can try to start with a yoga class or something like that, because at the end of the day yoga is mostly meditation and focus on breath. Meditating is also extremely important in welfare for everyone, especially entrepreneurs and founders. The daily stress of running a startup can not only get you down, but also lead to feeling lost.
I don't know what drugs you are on, but I can recommend some supplements and nootropics that will definitely elevate mood. Try tyrosine.