Sleep is super important.
Most people (funnily enough, those who are not chronically sleep deprived) will feel a marked difference when losing as little as an hour of sleep a night. The differences usually include being easily stressed out, angered or emotional, losing cognitive function (slower to react, reaching for words, forgetting things, etc), and just being less happy. Also, sleeping time is essential time for the body to repair, heal, clean house. When we disturb that process, we are putting ourselves in harms way by weakening our immune response and not allowing the intelligence of this amazing body to do its thang.