This will vary across patients. For some they may only be vaguely aware of what is going on or have a vague memory of what happened. For example, they may recall lights, noises, or a few words said.
In more serious cases the patient may feel pressure or pain and have trouble breathing. Some patients describe a feeling of panic.
Can you feel pain during anaesthesia awareness?
Not all people who suffer anaesthesia awareness will feel pain, but some may. The level of pain will vary from patient to patient.