Once I walled up all the entrances and thought that I'm safe. I managed to make the fortress quite stable, i.e. resources are replenished by dwarves and they always stay happy.
But eventually I started to lose dwarves faster than they breed. This is a list of causes of deaths in a sealed fortress which are easy to forget about. Please help me amend it:
Dwarf is scared to death by a ghost which I forgot to bury before sealing the fortress.
After few years clothes fell apart, which caused surprisingly severe bad thoughts and led to tantrum spiral.
Dwarf fell into strange mood while I did not have a certain type of workshop. He went insane.
One of dwarves turned out to be a vampire and killed a number of dwarves before he was caught. Moreover, I had to kill the vampire as well, i.e. lost one dwarf more.
So, what can be added to this list? What else to beware of?