Thanks for the query. Some of the reasons for excessive sleep are- Insufficient quality or quantity of night time sleep. Misalignments of the body s circadian pacemaker with the environment. Another underlying sleep disorder, such as narcolepsy, sleep apnoea, idiopathic hypersomnia or restless legs syndrome. Disorders such as clinical depression or atypical depression. Tumors, head trauma, anemia, kidney failure, hypothyroidism or an injury to the central nervous system. Drug abuse. Genetic predisposition. If he is active, gaining weight, passing urine stool normaly there is nothing to worry. Hope i helped you.