Heart felt like it stopped while falling asleep

Sounds like it could be one of two things. The first one is simply good old ectopic beats which you've experienced in the past, I get them, and for me they always feel like my heart stops for a second or so before then restarting, hence the whole "missed beats" expression, these can be especially pronounced as you're about to go to sleep, as this is when your heart is changing speed & also, you're more in tune with what your body's doing because you've got no distractions.

The other thing it could be has nothing to do with your heart even though it may feel as such, do some research on 'hypnic jerks'.

Doesn't sound like anything to worry too much about but it may be worth getting another holter, maybe a 7 day one.

Other than PVCs and occasional PACs, have your multiple cardio tests showed anything else? If not, I wouldn't worry about it and discuss it at your appointment in two months.