I figured out how to swap between accounts ok. But, on some occasions I have accidentally logged out on one of the accounts. The only way to get back into that account seems to be to restart Windows. Is there any other solution?

BTW it's usually the main account I usually accidentally log out of but I suspect it does not matter, once logged out you cannot log back in until a restart. Surely there's another option?

Another downside of accidental log-outs is if you have programs running, Windows does not ask if you wish to close them first, etc. (unless you have unsaved documents I guess.)

I've discovered with Birdy's help that my main account is the administrator account, thus once I log out of it, it vanishes until I reboot. I should set up a new account and transfer the profile across to fix the issue. I did not know we are not suppose to use the main administrator account as a regular log-in account.