If you can tolerate a beta blocker, that might help to eliminate some of the shakiness you're experiencing. Beta blockers can lessen the effect of adrenaline on your body. Laying down for a few minutes might be helpful as well.
Sorry I can't be of more help at the moment, but hopefully someone else in our community will have some ideas for you.
Unfortunately, I personally haven't found anything in particular that alleviates the tremulousness. The best thing I can tell you is that if misery loves company, you've found it here--LOTS of people with POTS have that symptom. :-/
You may find at some point that one medication or another (as Halbashes suggested, a Beta Blocker is likely) may lessen these types of symptoms; you may also find that certain things tend to worsen and trigger them. Some people are particularly susceptible to stimulants like caffeine or the ingredients in some over the counter cough/cold medicines. If you notice these things are exacerbating the tremulousness, you may be able to control it better by making lifestyle changes to avoid certain substances.
That's my 2¢, hopefully others will have more ideas!
I have had almost no shakiness since starting Mestinon a few years ago. Occassionally I'll get a really bad episode where I drop what I'm holding and have to lie down, but it has become pretty rare. Can't tell you why it works, but it sure does for me.