I have had, on the odd occasion, a kind of 'temporary perfect pitch' but it doesn't last. I've noticed it when well into a tunes session, having gotten into a conversation with someone and hearing a tune being played which I did not know, I knew which key it was in and could identify notes as they were played. I probably couldn't do this at the start of the session and of course not at the end if I got too relaxed. It was an interesting experience.