What does it feel like to be hypnotised?
Most simply feel very relaxed; they're generally aware of everything being said to them, and usually hear background noises etc. Often there is a sensation of "floating" or bodily lightness, but sometimes the limbs/body may feel very heavy. Frequently there is increased lachrymation (eye watering), and when the eyes are closed there is usually rapid eye movement; in some cases the eyes invert - roll up into the head.
People in hypnosis are in a hyper-attentive state: they're usually very focused on the hypnotist's voice which may seem to be "inside" their heads, or in some cases to be coming from far away. Although people in hypnosis can and do move, there is a general lassitude/disinclination to move unless instructed to do so. Most will display "trance logic" - i.e. behave in accordance with the suggestions made to them rather than reacting to objective reality. For example, if the hypnotist suggests it's cold the subject may shiver/hug him/herself even though the ambient room temperature is comfortably warm.
Many people experience some degree of time distortion - frequently the time passed in trance will seem much less than was actually the case, but sometimes the opposite pertains.
Most people do not experience amnesia, but some do, remembering nothing specific about what happened whilst in hypnosis. Generally, the more frequently someone is hypnotised the more likely it is they'll develop trance amnesia. Not remembering what was said in trance will not affect the effectiveness.
Some people enter hypnosis very easily, and these are most likely to experience the full range of hypnotic phenomena: they may become somnambulistic and able to open their eyes, walk around, perform tasks etc whilst still remaining in a deep trance. If suggested to them, they may experience hallucinations, anaesthesia, bodily catalepsy, etc..
When first hypnotised many do not think they were hypnotised at all. For many, hypnosis is not unlike a "daydream" - and, in truth, that's really all it is, but one induced deliberately rather than occurring spontaneously and one with a hugely powerful outcome.