Please find more about orexin: https://en.wikipedia.org/wiki/Orexin

Let me quote: Orexin (/ɒˈrɛksɪn/), also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite.[1] The most common form of narcolepsy, type 1, in which the sufferer experiences brief losses of muscle tone (cataplexy), is caused by a lack of orexin in the brain due to destruction of the cells that produce it.

And another quote: Orexin-producing cells have recently been shown to be inhibited by leptin (through the leptin receptor pathway), but are activated by ghrelin and hypoglycemia (glucose inhibits orexin production).

To have a good sleep you probably need relatively high glucose level.

Liver and muscles have enough storage of glucose. Low levels of insulin and glucose are pretty important for cardiovascular and liver health. IIRC, some recovery processes and hormone levels in our body depend on the glucose levels and we want to have them during the whole sleep.