When I feel tired, I most probably get a very sound sleep that very night. I understand that as and when we feel tired, we don't neccessarily have the liberty to take a nap. Say, if I feel tired at my workplace, (and that's usually coz I'd have slept late the night before), I get up, wash my face, talk up to a friend/colleague, and at times, I read up something apart from work. (Like visiting these forums
) I try to focus on something else, anything.
TBH, it normally means to ignore the body's need to relax now and make up for it in the night/later part of the day. I am not sure if that's the best practice, but it's like a quickfix.
One another thing that I suppose leads to me feeling tired, in the sense having an aching in some areas of the body, giving off the feel of lethargy is a bad posture. I am hooked on my pc atleast for 10-11 hrs a day. It surely plays a role here and there. So I believe a proper posture, maybe while you're studying and researching, should play a role. And an extended listening to music with the headphones on also makes me feel lethargic to an extent. Somehow. So I tend to avoiding this.