Did my computer diagnose & fix itself while shut down or was this just a glitch that went away?

I’ve got a Dell Inspirion laptop that I bought at the beginning of the year. Aside from it being disfigured by Windows 10, I hadn’t had any issues with it. Two days ago when I turned it on, there was a message from Dell saying my machine seemed to be having trouble starting and that it didn’t recognize the power source and the battery might not charge and pestilence and famine was sure to follow. It started a series of diagnostics full of loud beeps and color bars, then informed me the next diagnostic would last 3 hours. I did not have 3 hours before work, and I was unwilling to leave it turned on and plugged in, so I exited. I did check the cords and try restarting it on battery and in a different outlet, but the same message appeared. It was going to be this morning before I could devote the time to babysitting it, so I turned it on, and it’s fine.

Um…what happened?

Well perhaps turning it off and on again finally worked.

See, that’s what I was hoping, but I’ve never had a Dell so I wasn’t sure what their “An error occurred–wait never mind” message looked like.