Was taking 2.5mg lupin every 12hr. diasbp was high 90s later in day so cardiologist said take 5mg in am. skipped a dose, started 5mg. bp dropped to 50?

50 is low: Sounds like you doctor has a good plan but 50 is low for diastolic (depending on other factors as well). This is a perfect opportunity to follow up with you doctor - good job for measuring your BP and noticing a problem. It can take a while to get BP management "just right". Hang in there and communicate with your internist.

Talk to your doctor.: In general, medical articles recommend gradual reduction of blood pressure especially for elderly patients as it may cause a stroke and/or other blood pressure related conditions due to very low blood pressures. Allowing elevated blood pressures maybe considered on a case by case basis. I recommend that you talk to your cardiologist to determine what the goal blood pressure is.