I feel really bad..

So I have both POTS and a number of anxiety disorders. POTS is an illness where your heart rate skyrockets when you stand, resulting in a lot of symptoms that are similar to anxiety symptoms (dizziness, shakiness, nausea, vision problems).
ANYWAY, I had to quit school and work due to the severity of this illness, and since then I've found that the symptoms of it come and go.
However, I have developed a fear of going in public places, especially stores, because I'm worried I will get an episode of either POTS or panic (it's hard for me to determine which my episodes are because they are so similar in nature) so I have been sitting at home a lot.
Today, I went to my grandma's and was super nervous I would get sick while I was there, until right before I was going to leave when I stood up and my vision blacked out, heart rate skyrocketed, and I felt like I was going to faint. I was very shook up and left, but felt strange afterward for about an hour.
I went home and waited for my boyfriend to get home from work. During that time, I realized that thanksgiving is tomorrow and that I have to spend the whole day at his grandparents and got incredibly nervous that I would get sick around his family. I also began to feel better, symptom wise.
He got home, and I acted like I was still dizzy and sick, like how I was a couple hours before, even though I wasn't at that time. I was trying to, for lack of better terms, fake sick to get out of going to thanksgiving tomorrow. He bought it and gave me the ok to not come, though he was a little upset and I think I also made him nervous about my health because I exaggerated my current sickness level to him a bit.
Now I feel TERRIBLE and am sitting here thinking how I am basically a POS, evil person deep down with terrible motives for everything I do.
I NEED YOUR THOUGHTS. THANKS

First, you are definitely not an 'evil person', I have done something quite similar (I don't have POTS, however I do have extreme anxiety.) I of course at the time felt terrible about it, however I hadn't done anything to fix that -which now I deeply regret- perhaps try to talk it out with him, tell him your concerns. That way, he can help you through it. I haven't necessarily told anyone my concerns, (including not liking to go to parties, because I don't want to get anxious.) And, due to this -no one knows it makes me uncomfortable, so they continue to take me- what I am trying to say at this point is, reaching out to someone you trust, (my grandma is the one I trust the most, in which I normally tell her about my concerns.)
Will allow them to help you push through this.
Don't fret, everyone just needs a helping hand every now and again!

I'm so sorry that you feel terrible. I agree, everyone needs a little help now and then! There's nothing wrong with how you're experiencing this. There may not be a simple answer, but you will be ok. When you have more minor-level panic attacks, are you able to use any grounding techniques? I shared 54321 grounding on the thread above:
Name five things you can see in the room with you.
Name four things you can feel.
Name three things you can hear right now.
Name two things you can smell right now.
Name one good thing about yourself.

I know that this won't help with many panic attacks or with POTS, but it may help when you're expereincing anxity about the holiday or other things, to try to keep you otherwise relaxed.

I have a bag of objects that invoke those 5 senses. It is helping. My anxiety is sometimes so bad I think catastrophically too. I have lied at times to get out of doing something I am too anxious to do.