You know, when in Ultima 6 and its spinoffs you take manual control of a character and the other doesn't follow, and you can't sleep or enter combat. How do I get out of it?

If the party is all together, pressing the 0 (zero) key should return them to party mode. It won't work if someone in the party isn't present.

Alternatively, if the solo mode character gets killed, the game will switch back to party mode.

Exception: If you cast Armageddon, the game will not switch back to party mode; if this happens when you're controlling someone other than the avatar, the game will go into an infinite loop and softlock. (Might be fun to try this at least once (try placing the spell on a staff), but make sure you save first.)