My mother had a colonoscopy at 8am this morning, it is now 3pm and she is nauseous and light headed. she has not been able to keep liquids down.

Anesthesia : When you have a colonoscopy, you are under IV sedation anesthesia. Some people are more sensitive than others and can have side effects like those experienced by your mother. Fortunately, these should resolve over the next 24 hours. If this becomes prolonged and persistent over 2 -3 days, then you should contact the doctor who did the procedure.