I suddenly started having issues connecting to my EC2 instance, and in the AWS console, I noticed the instance status was stopped.
I am not very familiar with AWS EC2, but if I understand correctly, EC2 instances don't stop on their own, so I must have triggered it somehow. How could this happen? Could it have errored out somehow, or did someone have to explicitly stop it?
AWS doesn't take any action by own; there might a possibility you have triggered it by mistake. Since you can start it again also you can set one cloudwatch alarm to get more notification about the running Instance.
At the same time, you can create one topic for SNS and subscribe to it via email. so that if anything happens with your instance it will notify you or you can set the action for all the available events