Impressions for orthodontic analysis can be taken in two ways – the standard way, using impression material, or by intraoral scanning. When we use impression material, we place a type of silicone in the mouth for a few minutes. It can't really be called unpleasant, but in some patients it does cause gagging when the impression of the upper jaw is taken.
Patients describe having an impression taken with an intraoral scanner as quicker and more pleasant. No silicone is placed in the mouth, and it doesn't cause gagging or irritation. The patient may notice their mouth drying out slightly during the procedure.
This answer is for general information. Your own case needs an examination by an orthodontist.