do you mean - is it possible to have flashbacks when you are half asleep. yes. flashbacks can happen at any time.

Sometimes flashbacks during the half asleep mode is called having an hallucination depending on the accompanying symptoms.

only your treatment provider can tell you whether what you experienced was a flashback or an hallucination.

are flashbacks like a nightmare no. in order to have a nightmare you must be asleep and in the sleep cycle known as REM. thats when a person can dream. flashbacks dont happen during sleep cycles, that I know of anyway.