Dr prescribed thorazine (chlorpromazine) for insomnia. is this dangerous?

Not necessarily: Thorazine (chlorpromazine) is an antipsychotic medication with strong sedative properties -- that it can cause drowsiness. If you are also having psychotic symptoms such as hallucinations and delusions along with insomnia, it may be helpful. Thorazine (chlorpromazine) isn't usually used for insomnia alone, though, as side effects like movement disorders and restlessness can result. It may help you sleep more than Risperdal will.