You have given us an amazing description of your symptoms.
You express so clearly, every mechanism that anxiety and panic attacks can trigger. Not just panic attacks (that was the first one) but the somewhat sustained alert mechanisms in your body that is triggered by a sustained fear that your heart is not OK. I know them extremely well. They all match mine. The exercise intolerance. The anxiety. The blood pressure when standing. The variable heart rate when changing positions. The palpitations and discomfort when standing. And funny enough, I have somewhat low blood pressure, I take Pranolol 10 mg x 2 and I've quit chewing tobacco (my girlfriend gave me the choice, that or her ;) I think I can relate to this.
To give you some clear answers: (I know that only doctors can do that, but I'll take that chance, because this is REALLY clear)
1. What you felt the first time was a panic attack. Pranolol will usually remove those. Some therapy might help as well. Arrhythmias don't increase and decrease, they hit like BAM and goes away from one heartbeat to the next. And your symptoms completely match panic attacks. The rate of 170 BPM is not especially high during panic attacks, it can go far above 200.
2. Your blood pressure is probably not elevated when you stand up. It's the measuring during a new setting that scares you and that elevates the blood pressure (probably). I did measure BP up to 150/90 when standing, and 120/70 when sitting. When a doctor measured them both in a stressed setting (when the resting blood pressure was high too) she found a systolic drop of 10-15 mmhg. Normal.
3. The heart rate is supposed to increase when you change from supine position to sitting, standing, turning around in bed, bending down, etc. But your awareness will make the body "think" like: This is dangerous, so I need to increase my heart rate (and blood pressure) even more when I do this. The sooner you lose attention to it, the sooner it will reduce to normal response.
4. I think it's uncomfortable to walk up stairs, not the walking, but the feeling of increased heart rate afterwards. It's a normal response. Everyone get a high heart rate in the beginning of exercise (and it will slow after a minute or so) because it takes time to increase the stroke volume in the heart (it takes some time for enough blood to run back, to properly fill the heart). The heart compensates by increasing the heart rate. Again, with anxiety, the effect will be stronger. It's fairly normal that the heart rate drops quickly after this, but it can also be sustained high if the anxiety gets you. The reason why it can drop quickly is that it's only a nervous stimulation (parasympathic) that causes the heart rate to increase, you don't have high adrenaline levels yet (again: unless you are anxious) and it's quickly reversable with vagal stimulation.
5. We can all get a little dizzy in the shower. The blood vessels dilate due to temperature increase and blood pressure can drop. I'm really familiar with that one.
6. Try to exercise, but if the doctor prescribed propranolol, try to exercise an hour or so after taking one. It really helps. If the blood pressure is a little low, try to avoid exercise right after meals (as you can get a little dizzy because more blood is directed to your GI tract).
Good luck!!!!!!!! Do NOT be afraid of this! :)
It sure seems to me to be a full blown panic attack, you have every symptom of one, and I can speak from experience, I have had them and they come on and affect me the exact same way. They can come out of nowhere at times. Your system is probably going through a type of withdrawal from the chewing tobacco and it is causing all these horrid symptoms.
When you are in a state of anxiety, just the simple task of walking can cause breathlessness as you are sub-consciously holding yourself tight and this causes all muscles etc to be tight and can affect the breathing. Of course, being inactive does contribute some, but not all.
Anxiety about the heart and other symptoms is causing a vicious circle, the more anxious you are about the feelings, the worse the feelings become. There are two very good books that will help you, they are by Dr Claire Weekes, one is called "Hope and help for your Nerves" and the other is called "Peace from Nervous Suffering" They are written in every day language and very easy to understand, I would be lost with out mine.
If the anxiety gets to the point of unbearable, which is sounds close to already, you might want to see your doctor and have a general check up and some blood drawn. You could even have some Low Blood Sugar, this can also cause the anxiety. Try to remain clam, I know, easier said than done, and try to think of other things that make you happy.
I hope this helps and good luck, keep us posted as to how you are doing.