wow sounds like my second pregnancy LOL except that the majority of my pulse problems were in my first pregnancy
1st off I know EXACTLY how you feel with the pulse thing. I had the EXACT same thing. Episodes would last roughly 45-60 minutes and the hospital would never catch it (except once)... Thyroid come back normal (its a symptomn of that), I wasn't dehydrated (again its a symptomn of that) thus it was either asthma attacks (which I do have asthma and it is a symptomn of that) or PE (again another symtpomn)
In my second pregnancy I would get really high readings and rush to the hosptial feeling dizzy and having a headache, they would lay me down, take my BP and of course it dropped and since I didn't have protein they would start reciting the medical books (Hi, do I look like you medical book?!?)
But, they were wrong, though there wasn't anything they could really do about it and when I gianed 7-10 lbs in 8 days and had a BP reading at my docs office of 120/98 she decided we had fooled around with it long enough.
Of my symptomns all my doctor could say was that I exhibited symptomns abnormally and it looked like my body was more intune to my BP. Thus, instead of having problems at 140/90 I started having problems at 130/84.
As for advice, if you don't feel well just keep going. It doesn't matter if the doctors think your wrong, a hyperchondriac, nuts whatever, because when it comes right down to it if something DOES happen, its YOU that it happens too. Also, talk to your regular doctor and your insurance. You may be able to get someone to come out and monitor your BP to report to the doctor etc..
The thing about position, sitting up and standing the baby shouldn't be laying on your artery unless the baby is in a strange position, but laying down on your back then the baby will (also think about how could the baby by putting pressure on the artery unless the artery runs sidewise underneath the baby when your sitting up/standing)
Your BP DOES drop when lying down on your side, I am a good example of that. In labor with my second child they monitored my BP every 5 mins the entire time. It stayed at 125/70 at all times EXCEPT when I either sat up, stood up, or rolled over to my back. Every single time it shot to 140/90.
In addition, if standing up/sitting caused the baby to place pressure on the artery, then all pregnant woman would have their BP's skyrocket when standing and they don't.
Hope it helps, your not the first person who's gone through something like this. There are those of us out there that exhibit symptomns differently and when doctors see us, they tend to ignore it becuase its atypical and think its something else even though its not.
Mommy to Alex and Mason