At night, some of my fingers become very stiff. often, in the morning, i have to manually straighten them out. what is happening?

Unclear: Without a more thorough history and without examining you, it is difficult to determine what is happening. You may have a trigger finger which reveals itself mostly while you sleep and you notice it when you awaken. I'd recommend you see a hand surgeon before things get worse.

Maybe trigger finger: It's hard to tell without seeing you in person, but trigger fingers or arthritis cause what you are describing. See a hand surgeon who can examine you and get x-rays. Good luck!