It is awful to be rushed out isn't it . I have had both with and without US guided. One of my worst experiences with ET (had 6 now) was with US and I found myself actually zone out mentally for the experience as it was so awful. I would have prefered no US in that situation TBH.

There is no way the embryo can fall out when you stand up, it is a pretty viscous environment that would overcome gravity, let alone there is almost no space in there. They should check both the catheta and the catheta contents after ET to see if the embryo was discharged before letting you get up and go. I think having your legs up and rest can help if the cervix or uterus has undergone a bit of trauma during ET and it may reduces any spasms but that can also be done in a chair afterwards. In my experience if you insist on lying there for a few moments or minutes to compose yourself even the most rushed clinics will let you. That said I have also jumped up and off the bed straight after and gone straight to the car and out shopping!

Modern science has gotten you this far hun, it is now the horrible waiting game to let nature do its thing. I HTH and wishing you all the best.
xx