I totally know how you feel, I get like that sometimes for up to a week! It is very hard to get motivated to do anything, but I used to have a routine of going to the gym at least 5 times a week and during that time I always had energy, since I stopped I feel drained most of the time. That is only my solution, just to get as much motivation as you can to excercise, that is what helps me but it also may be different for you. Someone else may have other solutions that could work better for you.