Melatonin can cause somnolence (drowsiness), and, therefore, caution should be shown when driving, operating machinery, etc.
en.wikipedia.org It can manifest as somnolence, lethargy, or directed attention fatigue.
en.wikipedia.org Its symptoms can include somnolence (drowsiness) and, in extreme cases, coma.
en.wikipedia.org Agonists produce significant, although mild, side effects including somnolence, hallucinations, insomnia, nausea, and constipation.
en.wikipedia.org More severe forms of hepatic encephalopathy lead to a worsening level of consciousness, from lethargy to somnolence and eventually coma.
en.wikipedia.org