Inside the shower head is a plastic or rubber washer that restricts the water pressure and causes it to be less than adequate. If you have recently installed a new shower head, remove it and look into the threaded tube to see if there is a water saving device installed. If so, you can make the hole in the washer bigger by using a drill or completely remove it using a screwdriver. Once removed or made bigger, install it back on the shower and test to see if the water pressure has improved.
A homemade shower with pressure. 2 gallon sprayer plus a shower head (or kitchen sprayer) and a fitting. Directions are included here. They put in 1 gallon of tap water and 1/2 gallon of boiling water to get the right temp. They are considering painting it black and putting it outside to make a solar shower. Very clever!
hypotension. Eat a diet higher in salt. Drink lots of nonalcoholic fluids. Elevate the head of your bed at night. Avoid straining while on the toilet.Avoid prolonged exposure to hot water, such as hot showers and spas. If you get dizzy, sit down. It may be helpful to keep a chair or stool in the shower in case you need to sit; to help prevent injury, use a nonslip chair or stool designed for use in showers and bath tubs.http://www.webmd.com/heart/understanding-low-blood-pressure-treatment