My achy breaky heart

About a week ago, while wandering around aimlessly at Rite Aid, I came across one of those blood pressure testing machines.
I used to use them for fun when I was young while mom took her sweet time getting her prescriptions filled. Back then, I never put any stock into the actual read-outs.
So I'm now 20, coming up on 21, and I decided to give it a shot. I was expecting some underwhelming results that meant nothing, but then I realized that my readings were sort of... bad.
According to the machine, I'm developing pre-hypertension, and my heart rate is about 10 bpm too high.

Even without this read-out, I've known for the last few years my heart isn't as strong as it should be. My resting heart rate is actually quite fast, even when I'm completely chill. Concerning to say the least.

I've been stuck at my mom's place in Virginia Beach for the past few weeks. I say "stuck" because what started out to be a two-week vacation has shaped up to be three weeks of tension being sandwiched between my mom and her neurotic asshole boyfriend, and I'm about ready to go the fuck home already. My only escape is the beach itself.

A couple of days ago I spent pretty much the entire day swimming in the churning surf under a skin-blisteringly hot sun. I felt pretty great until I got home and took a shower.
Suddenly I was really lightheaded, my heart was pounding, and I felt like I couldn't breathe. I didn't pass out, but I was damn close.
Mom, who's a nurse, said it could be dehydration. Spending the day marinating in salt water under a sweltering sun definitely takes it's toll. But even after drinking half a gallon of water and gatorade; my palpitations persisted, as did my dizziness and trouble breathing.

Mom gave me an anti-anxiety pill, and I crashed hard on the couch. It was a couple of hours before I felt well enough to stand. My heart rate isn't nearly as high now, but it's definitely still well over what a healthy bpm should be.

My friend Joe told me that me taking a hot shower after a day of exercise can cause my blood vessels to dilate and it basically floods my heart. This makes it work double-time and can cause dizziness and fatigue. This seems like a probable cause, but I know that my heart - in general - needs to be healthier.

I don't exercise nearly as much as I would like to, and the little exercise I do get is usually sort of rigorous.

I don't know if this is related or not, but about a week ago I passed out while doing my morning stretches and I have no idea why. I was only out for a minute, but I had definitely just fainted like a bitch mid-stretch. One second I was stretching, the next I was on the floor with a head ache and a big gash in my arm. No conscious memory of the actual fall taking place.

I don't smoke, drink, or do drugs (often). I eat relatively healthy too. I barely exercise, and I think that's the main cause for these health issues. I'm going to schedule an appointment with a cardiologist when I'm back home, and get on a more regular exercise regimen.

TLDR: My heart hates me.

Thoughts? Opinions? Related stories?