Flexeril is a muscle relaxant, but the biggest side effect that people complain of is either fatigue or sluggishness - "foggy thinking". Unfortunately, all of the muscle relaxers can do this to some degree, including Soma, Norflex, Skelaxin, Robaxin, Zanaflex, etc. If they're really helping you, I guess it's worth the trade off; if it's scaring you, I would probably ask for a trial of a different med. Muscle relaxers are more for spasms and stiffness than for pain relief anyway.