DVLA usually get the forms to you 54 days before your entitlement expires which should be enough time to get your medical sorted.
Try some relaxation, getting stressed will only raise your blood pressure which is not helpful. Try and get an appointment with your local medical practice nurse to give you a session of blood pressure tests to get you used to them, I found it very helpful. I have a BP tester at home and coming up to my medical I always take my BP for a few days previous to settle myself down, and if it is slightly high when I go for my medical, I always tell the quack what my home monitoring is and he write it on the D4, never had a problem.