Fludrocortisone and Midodrine are both medications that can help raise blood pressure. Ask your physician if one of these medications would be right for your situation. People are not generally prescribed medicine for low blood pressure, as it's not often a cause for concern unless it presents with symptoms.
Why do the middle fingers lock up when experiencing pain in neck and shoulders?   One cause could be some kind of impingement (pressure or swelling that applies pressure) of the spinal cord at C7, one of the cervical segments of your spine.
Often, patients wake up to find their affected finger or thumb in a locked flexed position, which creates a restless sleep pattern. Furthermore, trigger fingers and thumbs creak upon flexion and extension. The cause of trigger finger or thumb is repetitive movement, with increased degrees of motion, time and clenching.