Magic mushroom trips flashbacks possible?

Yes: I've had pts who described having them valium calmed them down.

Yes, but it's rare: Psilocybin and psilocyn are the hallucinogenic elements in certain mushrooms. These “magic” mushrooms usually cause nausea before any desired mental effects. People who ingest them often experience distorted perceptions of touch, sight, sound, and taste. Some users become very nervous and paranoid. On occasion, they can also experience "flashbacks" or hallucinogen persisting perception disorder.