We don't sleep at the right time, we will sleep at the wrong time (Based on Gita 06.16)
When practicing spiritual life, we may equate spiritual advancement with denying our bodily needs such as sleep. We may deprive ourselves of sleep to demonstrate our spiritual advancement.
However, spiritual advancement centers not on physical deprivation, but on spiritual absorption. To grow spiritually, we need to become conscious of our own spiritual identity and of the supreme spiritual reality, Krishna. The more we become lovingly absorbed in Krishna, the more we advance spiritually.
We can cultivate divine absorption by practicing bhakti-yoga. For such yoga practice, our body is a vital tool. It's like a vehicle; if it isn't fuelled, it can't function. Food and sleep are basic needs of the body. If we don't sleep adequately, we won't be able to think clearly or act properly – and we won't be able to practice yoga. Pertinently, the Bhagavad-gita (06.17) states that even forest-dwelling yogis who have renounced the world need to be regulated in their sleeping. If we deprive ourselves of sleep, we will find ourselves sleeping at the wrong time, for example when we are studying scripture or chanting holy names – or, dangerously, when we are driving. If we sleep inadequately, our mind will go crazy. If we sleep excessively, our mind will become lazy. Either way, our mind won't be receptive to yoga practice.
Still, don't we need to restrict bodily gratification? Yes, but gratifying the body is different from caring for it. Gratifying the body is like getting so obsessed with the car that we forget about driving to our destination. When we are balanced, we don't pander to the body so much that we forget our spiritual purpose; but we keep it fit to pursue our spiritual purpose.
To conclude, don't deprive the body – and don't let the body deprive the soul.
Verse 06.16 – "There is no possibility of one's becoming a yogi, O Arjuna, if one eats too much or eats too little, sleeps too much or does not sleep enough."