Repeated and multiple arousals (of which the person is usually unaware) result in an abnormal sleep architecture and daytime somnolence (sleepiness).
en.wikipedia.org Possible side effects include abdominal pain, allergy, diarrhea, headache, hepatic dysfunction/hepatitis, nausea or vomiting, exacerbation of porphyries, pruritis, rash, somnolence, vertigo, or dizziness.
en.wikipedia.org It can manifest as somnolence, lethargy, or directed attention fatigue.
en.wikipedia.org Drowsiness, somnolence, fatigue, and vertigo have also been seen.
en.wikipedia.org The most common treatment-emergent adverse effects reported with use of the drug include insomnia, nausea, headache, somnolence, affect lability and blood creatine phosphokinase increase.
en.wikipedia.org