After a long, hard day of fending off primitive monsters, donating blood, and cleansing rooms of fecal matter, Isaac can feel a bit drowsy and weak. If he wears this comfy hat as he descends into a new floor of his basement, he can get a much better sleep on the ground (aside from his agonizing nightmares, of course), restoring his red health completely!

You can find the Nightcap on sale in shops.