Praise be to Allah.
Our contemporary scholars have ruled that the issue of hypnosis (hypnotherapy) has something to do with using the help of the jinn , and based on that we must note the following two points:
1– It is not permissible to seek the help of the jinn or any other creatures in trying to find out matters of the unseen, whether that is by calling upon them, trying to please them or any other method. Rather that is shirk because this is a kind of worship, and Allah has taught His slaves to worship Him ِlone and say, “You (Alone) we worship, and You (Alone) we ask for help (for each and everything)” [al-Fatihah 1:5 – interpretation of the meaning].
It was proven that the Prophet (peace and blessings of Allah be upon him) said to Ibn 'Abbas: “If you ask, then ask of Allah, and if you seek help, then seek help from Allah.” (Narrated by al-Tirmidhi, 2516)
2– Hypnosis is a kind of fortune-telling or magic whereby the hypnotist uses the jinn to overpower the subject and then speak through his tongue and give him strength to do things by means of controlling his faculties.
This is if the jinni is sincere towards the hypnotist and obeys him in return for the things by means of which the hypnotist draws close to him. So the jinni makes the subject obey the wishes of the hypnotist to do things or tell him things, through the help of the jinni.
Thus using hypnosis as a means of finding out where stolen goods are hidden, or where a lost item is, or as a means of treating disease or of doing anything else is not permissible. Rather it is shirk, for the reasons stated above, and because it implies turning to someone other than Allah and goes beyond the ordinary means which Allah has created for His creatures and permitted them to use.
And Allah knows best.