It could be described as the hands feeling weak. But it's more like my hands are stiff, and there's a spring that I'm having to press against to curl the fingers closed - it's harder to close them than normal.

It's not painful unless I try to force them closed all the way (though I've been having some aches & pains apart from this too - general hand achiness when I've slept too little and/or typed too much, and an occasional sharp burning pain in my right thumb.)

The stiffness seems to get worse during the night, instead of better (which makes me suspect rheumatoid arthritis). But it doesn't go away completely during the day either. This started happening in March, varying in intensity since then. So I'm wondering if it could be anything besides arthritis, as it seems odd for arthritis to come on so suddenly.