Could be just blockage by wax or something else. Only as examination of the ear will confirm this

A unilateral hearing loss is most often caused by a problem within the ear canal most often wax but also a canal infection A noise induced hearing loss would be gradual and may be associated with ringing. This would best be evaluated with an audiogram.

If it is a sudden hearing loss, then it is most likely viral attack of the hearing nerve (8th CN). However if it is long term then you should go and see a ENT immediately. Most hearing loss is symmetrical and unilateral hearing loss can sometimes be an acoustic neuroma which is a benign tumor of the 8th cranial nerve, or the hearing nerve. Both conditions need to be seen by an ENT.