Childhood Diseases

I hope you can help. My son is 4 and a half years old. He is in a nursery school, very happy end eager to go. He is also very clever and are performing well. The problem is he sleeping 12 hours every night and is always tired. He is also emotional very unstable and would laugh, cry and augh all with in 10 minutes. Sometimes when he cries about smething stupid. he can lie down and cry for up to an half an hour. We did some blood tests and it shows he is low in iron. His sugar and iroid is fine. Can this be iron or is he maybe a emotional nstable child. Me and my wife is stable ppl with good relaions . Please help.