There are also studies that suggest that sleep is done without clothing. It is claimed to make the body become more fresh.
So how does Islam view this?
In the Qur'an Letter An Nur verse 58, there are three times for someone to be asked for permission to be disturbed by others.
"O ye who believe! Let the slaves (men and women) whom ye have, and those who have not yet balighed among you, ask for your permission three times (in one day) namely: before the morning prayer, when You put off your outer garments in the middle of the day and after the Isha prayer. "There are three sins to you: There is no sin upon you and none for them apart from those three times, they serve you, You (of necessity) to some (others), Thus Allah explains the verses for you, and Allah is Knower, Wise.
The above verse signifies three times a person who should not be disturbed by either the child or another family. Three times that is before dawn, when alone with a wife or husband, or after isya which is the time to sleep.
While the matter related to not wearing clothes while sleeping, Ibn Kathir gives an explanation.
"In the qoilulah time (sleeping during the day) regular clothes are removed for sleeping with his wife."
Ibn Kathir's explanation shows that a person is allowed to sleep without wearing clothes if he is in his bedroom specifically and as long as he is not worried about others seeing his private parts.