Yeah I typically notice it happens at night however it's quite spastic when it wants to be.
But no problem it's not just your computer pretty much everyone will get blipped off the map then return, when you see the 'Crash' topic in General chat then you know it's not just you. But normally comes back on between 1 - 5 minutes or less, Though if it is just yourself usually a restart of the computer or modem works just fine.