I take klonopin (clonazepam) at bedtime to help me sleep and it helps, but my question is, is it normal to constantly feel sleepy throughout the next day?

Klonopin (clonazepam) Klonopin (clonazepam) does cause drowsiness. Its half life is pretty long. Half life means how long it stays in your body before it is excreted out. Other conditions can cause excessive daytime sleepines such as sleep apnea.