Hi there. The first question would be "how are you feeling?" If you are fine, then it seems that LC agrees with you.

Now I am NOT a medical professional, but I have asked one of the RN's who post here to come and see what she thinks.

In the meantime, here's what I found on the net and what I know about LCing and its effects:
Atenolol is a beta blocker whose action is to regulate heart beat and keep it from speeding up. This helps to lower blood pressure.

Since the LC plans and Atkins are both diuretic in nature, (you lose water from cells and systems) they also tend to lower blood pressure. You don't want that to happen too fast or too drastically. So I would think that you should go to a higher carb level right away, perhaps 50-60 grams per day. Consider eating several LC veggies - at least one with every meal and also dairy (cheese, cream). This will slow the weight loss but most importantly, it will not take your blood pressure too low.

The Protein Power Plan books advise that people on blood pressure medication should take is slowly (55 grams of carbs) and be monitored by their physicians.

So I think you will be fine for tonight but calling your doctor is a good idea. Go eat something if you start feeling tired or shaky or light-headed or nauseated. That usually means that you need more carbs than you are taking in.

I am sure that someone will be along with a more professional opinion, but please remember, this site is NOT for medical advice.

I think you'll be fine. But if you are really worried, eat a slice or two of bread or a potato or cookies. That will stop the ketosis and help your cells take up water again. You can start again when you feel more confident. But take it slowly.