This very much describes a feeling I've had in similar circumstances/context, with my T, but I wouldn't have known how to word it! 'Instant quicksand' - EXACTLY! I definitely think it has to do with attachment and 'infant stuff'.

During a massive rupture with T when we didn't speak for several weeks and she no longer felt 'there', I related to Goldie Hawn's character, Helen, in 'Death Becomes Her'... (know the one?!) 'I have a hole in my stomach!!'

Just wanted to say I relate, and that I think you did great to recognise the trigger like that and discuss it with your T before you left