In "Night Terrors," everyone except Data is slowly degenerating, due to a lack of REM sleep caused by alien transmissions within Tyken's Rift.
In one scene, Guinan fires a weapon at the ceiling of Ten Forward in order to try and stop a fight.
I wonder if this action by Guinan was partially caused by her mind being weakened. This sort of behavior doesn't seem particularly consistent with Guinan's character. It is true that she called security first, but if this were a normal day and a fight broke out, I find it hard to believe that she'd fire a weapon at the ceiling.
On the other hand, it's quite possible that El-Aurians need no REM sleep, or much less REM sleep than other humanoids, to function properly.