Shame on your doctor, he should support your arm while taking BP. When "you" hold your arm up, it causes muscles to be tense causing higher bloodpressure.
You need to sit in a chair, leaning back, relaxed, legs not crossed, for about 10 minutes. Take BP, wait 1-3 minutes repeat, wait again and repeat. Toss out first number and average the last 2. This is called taking BP according to protocol. Doctors do not take time to do things right, in and out and you are gone. This protocol method was given by a hypertension specialist.
Most of the time doctors or nurses take BP as soon as you sit down after walking a long ways from waiting room. BP meds are given based on resting BP.
I use a bloodpressure monitor that is self inflating. This allows me to take bloodpressure according to protocol. Also, I keep a record of BP readings and the doctor uses those to judge how well BP is under control.