Is it among the aadaab to sleep with a kurtah on?

Answer

Yes, do wear a kurtah even whilst sleeping. It seems immodest to sleep without a kurtah. We are not saying that it is impermissible to sleep without a kurtah. But the natural haya of a Muslim requires that we act modestly in all states and at all times. It is among the aadaab (etiquettes) of dignity, deportment and haya (modesty/shame)