Good One-- lilstar!
That inner strength you seek is already here, just by what you are saying, it's where it starts from.
I get hit with it too, I sometimes wake up feeling that way :(, but I also know that it passes and I also know that depression also lifts.
If I feel I'm really in trouble, I use my "safety plan", I have my emergency numbers. All you have to do is survive it, and it will pass. If it persists for too long, the doctor can help with medication adjustments.
I think you are doing excellent with this though.