If you are reading this, you might be in a situation where you can't access your Facebook account and is getting the following message:
"Account Temporarily Unavailable."
"Your account is currently unavailable due to a site issue. We expect this to be resolved shortly. Please try again in a few minutes."
This is normal, they are doing site maintenance and your account will be available after that.
Your friends will be able to access their account, that's because Facebook doesn't disable all the accounts all together to do maintenance. So don't worry.
Another error you might get after able to access your account after maintenance is "An error occurred. Please try again in a few minutes.". You get this error while trying to like something or comment.
This error will also be fixed within 2-3 mins.