Thanks for writing to Health Care magic, I am Dr , Muhammad Ahmad , I have read your question closely, I understand your concern and will be helping you with your health related problem.
Yes in my opinion too this is due to white coat hypertension
. Yes the readings can fluctuate this much. White coat hyper tension is actually caused by anxiety
of being in a doctor's clinic and fearing about what comes next and how dangerous a condition you might be having.
This anxiety makes a person to get adrenaline
rushes, and activates sympathetic system's fight and flight responses, this makes the blood pressure to rise and heart rate
to get more, some people may get very little response to white coat anxiety and some get very significant response just like your do get.
I would suggest you to keep checking your blood pressure regularly at home if that stays well within limit then you shouldn't be worried at all and consider it a normal white coat hyper tension which doesn't need any special treatment.
I hope this answered your question, If you have more queries I am happy to answer you.