This is an explanation of the interaction.

http://www.drugs.com/interactions-ch...56-0,2245-4717

Going further in that site is a list of all interactions possible with Artane. You have to click on the drug name to
move to the list.

Also more on this drug here:
http://en.wikipedia.org/wiki/Trihexyphenidyl

and:
http://www.nlm.nih.gov/medlineplus/d...s/a682160.html

This link reveals the FDA reported Medwatch results for Artane:
http://www.drugcite.com/?q=artane

You can click on the individual items on the list for more details.

Also, I searched your midodrine on Drugcite.com with these results:
http://www.drugcite.com/?q=ProAmatine

If you click on movement disorders, it will detail them, and they sound similar to your descriptions.
You should know that midodrine has been on a list at the FDA for discontinuance, for a long time. And it was actually terminated recently, and only reinstated when some doctors complained. If you have POTs... there are other treatments besides this drug for that. It is something to consider.
Only a very small fraction of adverse events make it to the FDA...so when one sees small numbers, that doesn't mean in reality that the reported issue is infrequent. It only means the doctor or hospital did not report. Many doctors do not report for liability reasons, thinking it strengthens evidence for a law suit.