How do you get your mojo back?

I feel as though i have lost my zest for life, fallen out of love with the world.
I have become anti social, dont leave my house unless its for work, eat very unhealthy, smoke and drink more than i should.
It was only a few months ago that i was out going to the gym every other day, going out for walks, running/ jogging, watching what i ate, not smoking, calling my friends going out and just all in all – acting like a 24 yr old should.
How do you get the care factor for life back? i hate that i am like this, but everytime i force myself to do things i used to, i end up resenting my time doing it… Has anyone else ever gone through a phase (if thats what it is) like this and how have you pulled yourself out of it??