Have you been diagnosed with Ehler-Danlos syndrome?
Did you have any hypertensive episodes PRIOR to starting the Ritalin treatment?
Can you describe in a greater detail the “pressure sensations” in the head – is it more on the back of the head, or more in the face? Do you experience any facial flushing?
You have mentioned that there is a significant variation in your blood pressure occasionally. Have you made sure you measure your blood pressure multiple times during the a day, and do it consistently?
Finally, while I do not have the same experiences, I have noticed that if I consume a stimulant (say, Modafinil), and experience any pressures in the head/chest, L-THEANINE seems to cancel it. As it is easy to buy, maybe give it a go – it might help reduce the symptoms, while you are searching for a better option. (For example: http://www.amazon.com/Doctors-Best-Suntheanine-L-Theanine-Vegetable/dp/B001OXTGVG .)