I've been taking Baclofen for several years now, and have upped my dosage from 20mg per day to 80 mg per day.
I don't have any side effects from it at all...I think
It might make me sleepy...but I'm so fatigued as it is, I wouldn't notice a little extra fatigue.
My daily dosage of Provigil takes care of my fatigue (mostly) and the baclofen takes care of my lower back spacticity (mostly) so I'm good to go