I thought I'd mention that even without prescription medications there are ways to treat OI, whether it's NMH (Neurally Mediated Hypotension) or POTS. Patients have been helped with extra salt, potassium and water, for example. Or lifestyle changes. For example, avoiding things that trigger my symptoms (e.g., heat, standing, sitting upright too long, etc.) helps me a lot. It's not really a treatment, it's an adaptation, but it's better than nothing. Here's one list of what helps -
http://www.dinet.org/what_helps.htm
Or maybe you have a mild case? I do understand that diagnosis can be confusing.
For me, the minute I saw the list of symptoms for NMH, I realized that I matched up with almost every one of them. And then the tilt table test confirmed it. At that point I had been undiagnosed for 5 years so it was nice to have an answer of some kind.
It's just a hunch but I would focus more on your symptoms than on the specific heart rate pattern. It's hard enough for doctors to interpret the data from a controlled tilt table test (plus there are false positives and false negatives) so I can't imagine trying to do a test on yourself and having it be 100% accurate. As taniaaust1 said, moving around changes your BP and heart rate. And you can do it subconsciously. I had to be told a couple times during my first tilt table test to stop moving my feet. I was completely unaware that I was moving.
Also, my symptoms do not come on immediately on standing so don't think that is a requirement for OI. (I think this is a confusion with the more common type of OH where you stand up and immediately see "stars" and get dizzy) It takes at least a few minutes before I start getting the dizziness, nausea, increased heart rate, shortness of breath, and so on. And on the tilt table test it took 20-30 minutes before I got that very sudden drop in BP and then passed out.
You mentioned having trouble raising your arms. I get that, too. It's a common trigger. Feeling crappy after taking a shower is another common problem since it combines standing and heat. Even with my treatment I still have to sit down to shower. And I also sit down to dry off after the shower. But before treatment it was worse - I would have to lie down after a shower on most days. And then lie down again after getting dressed.
The type of OI that I have is called many different names but back in 1995, when I first got my diagnosis, it was called Vasodepressor Syncope by Dr. Rowe. It's also called Vasovagal Syncope, Neurocardiogenic Syncope, and other names. At some point some doctors studying ME/CFS patients started using the name NMH because so many of us NEVER faint (syncope=faint) during their daily acitivities. We get lots of symptoms from the BP drop (hypotension) but we have time to sit down before fainting. I have only fainted twice in my life and both times were during the tilt table test. Having the word for "faint" in the diagnosis is misleading.
I don't know what you have read so far (and I hope this is not information overload) but here are some links:
http://www.research1st.com/2011/06/19/the-outs-and-ins-of-oi/
(an overview - note the part where it says experts don't agree on terminology)
http://emedicine.medscape.com/article/902155-overview#aw2aab6b2
(From Dr. Julian Stewart - he uses the term Chronic Orthostatic Intolerance,
see
http://emedicine.medscape.com/article/902155-overview#aw2aab6b3 and
scroll down for a list of symptoms)
http://www.cfids.org/about-cfids/orthostatic-intolerance.asp
(this page has links to the webinar and slides presented by Dr. Rowe)
http://www.dinet.org/index.htm
(mostly about POTS but there's some information about NMH/NCS/etc.)
I hope there is at least something useful in all this rambling!
If you have more questions feel free to ask. I'm happy to share what has worked for me but it may not work for others.