[True_Moose]

There is one of two things that could have happened.

1) If your intelligence is low, you probably got hit once or twice. Mindflayers drain Int by something like 3(?) a hit. Once you hit zero, you're dead.
2) I think there's someway that they kill you almost instantly. I had a f/m with 19 int who kept getting killed instantly.

Try casting chaotic commands to not get held, and draw them out one at a time. A couple of cloudkills or death spells can work wonders too.