I'm going through the same thing with Heros of Might and Magic 3. I've had to let it rest for a couple of days whenever i finish something, so I still have a life. Luckily, I'm falling asleep no matter what I'm doing around 1:am, so I never go to bed at 4:am after playing games.
Word to the wise: Don't put your elbow on the table and support your chin with your hand while playing one handed. Turns out there's a nerve there that can get inflamed and now I have this numbing feeling in my pinky finger and part of my ring finger. It takes a long time to heal and it's been over a month and I still have that numbing feeling. I've already gone to the doctor, so no concerns there.
I had exactly the same problem, except I experienced pins and needles in my little finger and ring finger. It took 6+ months for it to go, and I can still sometimes feel a slight sensation several years later. Now I always rest my left arm on a piece of foam, which has prevented any recurrence.
Ah so that was what that was. Like you it went away all by itself after six months or thereabouts so I didn't bother going to the doctor.