What experiences are impossible to bring back during a flashback?

I have a friend who suffers from horrible flashbacks and I have a question regarding flashbacks.  We know the types of experiences flashbacks can bring back such as certain smells, sounds, and emotions.

But are there certain types of experiences that cannot be brought back during a flashback such as feeling hungry, tired, thirsty, etc.?  The most important question I have here is, would that also include the completely altered and strange horrible mental states we experience in our dreams and nightmares?

These types of altered mental states during dreams and nightmares cannot be described.  They are entirely new experiences unlike any other.  They are not experiences like touch, smell, feelings, etc.  They are completely altered mental states.  So can those altered mental states be brought back and experienced during your waking life during a flashback or not?