Question

why do people with high blood pressure sweat a lot

Answer 1

Excessive amount of sweating( if you have high amount of BP) is due to one of the symptoms of BP 'Hypertension'. In most of the cases(most not all!) hypertension leads to a profuse amount of sweat.  

As you may know high blood pressure usually results to fatigue and even over indulgences which stimulates your sweaty(pant!) glands; especially in your arm pits, neck and face! Even your hand middle can be sweaty as well for some people. 

People suffering from these should drink a lot of water and eat their medicines regularly. Or matters can go even worst than this! Resulting no other option than dead! x(

Hope this answer helps, if it does vote it the briniest answer!

Answer 2

Hyperhidrosis is the condition of excessive perspiration in the whole of the body.

People may not sweat excessively because of the hypertension or higher blood pressure than  120/80 mm Hg.  They are not directly related.  It is possible that they get exhausted quicker than others, or they have anxiety (nervousness) and hence they sweat more.

Normally excessive sweating comes from excessive activity from thyroid or pituitary glands.
 
    Hyperthyroidism means due to the excessive hormones released by the thyroid (present in our neck) all the metabolic processes in the body get faster.  Thus the sweat glands secret more fluids.  Hence, even the sweat generation process becomes more.