“Why does it take so long to wake up from anesthesia?”

Obesity, obstructive sleep apnea, and advanced age are the primary reasons for slow awakening from general anesthesia, while medication doses and drug interactions play secondary roles.

I’m not sure how long you are speaking of. In general it takes somewhat longer to wake up from inhalational (gas) anesthesia than total IV anesthesia. There is some increase in awakening time if the surgery is longer, on the order of hours, for instance. But we are talking minutes here for most people. There may be some grogginess that persists for hours if a lot of pain medicine (narcotics) or sedative (like versed or Valium) was used.

From Christopher Creighton

People with metabolic problems (hypothyroidism), the elderly, etc., are prone to recover slowly.