What just happened to my Android S6?

I was watching a YouTube video on my phone this morning when all of a sudden it completely spazzed and started repeating the same sound over and over again like a broken record. All the controls were also unresponsive as I found out when I tried to shut it down. I was in a hurry so I decided to leave it in my room while I went to class and when I came back 3 hours later it was still going. I was also extremely hot and I got the bright idea to put it next to the open window (it's 33F here). A few seconds later I got a blank screen with some words on it that I didn't have time to read but I think the first one said maintenance. Can anyone tell me what happened to it?