So sorry your little Jupiter is going through something; I know you must be so scared. I so wish these little ones could tell us what's wrong.
It's so tough to say what's going on here. Did you do BAT testing w/ your regular vet (Bile Acid Testing) to at least get an idea about Liver Shunt...?
Regarding the "dream state" - is she standing up when that happens? This very much sounds like it could be seizure activity if she is truly not "present" while it's happening.
If syncope is suspected, did your vet do an EKG? That should be explored if indicated after stethoscope exam.
Also, bc of both the "dream state" and legs giving out - the UT vet should definitely palpate (and Xray, probably) the entire spine very thoroughly, and do full range-of-motion exam, most especially in the neck area. Yorkies are prone to AAI (atlantoaxial instability); it's probably not AAI - but bc it runs in yorkies, it should be crossed off the list. Link for AAI:
https://vcahospitals.com/know-your-p...axial-luxation