This is why the term "bad trip" was coined. LSD is a synthetic and very strong drug. In the beginning, people always took it with someone who didn't take it so they could keep them calm. LSD hasn't been pure in years -- it almost always has speed in it, which is why it's so hard to come down from it. It was, in fact, only pure for a very short time. Even in the 60's testing labs found much of it wasn't actually LSD at all and most of it was cut with speed. So two things are possibly happening: the first is, the drug was more than your particular neurotransmitters and personality can handle and your brain needs to calm down and return to normal functioning. The second, and most likely, problem since you didn't take a huge amount of it or mix lots of drugs together is that, when a drug brings anxiety out of us, we then, if we're prone to anxious thinking, expect it to happen again when we feel similarly. If it continues much longer, one way to cut this off at the pass is to see a psychologist and work through it so it doesn't become a chronic way of thinking. If you can chock it up to experience on your own, then that's good, too. Drugs affect different people very differently; that includes pharmaceutical products, which LSD originally was. Just avoid drugs for awhile, and at your age, your brain is a bit young for this kind of thing anyway -- we know more about brains now than in the 60's, though not a ton more, and what we know is that young brains aren't fully developed yet. So don't mess with it too much. And don't go running to other drugs for more magic pills -- there aren't any. Sometimes they're necessary, but they're never magic. And if you must do drugs when you get older, stick to the natural ones, not the human-made ones. Peace.
My bad, I failed to mention I was with a friend and the beginning, it simply says I was with "him". I typed this all up on my phone so I might have made a few errors. Also for some reason my account says I'm female, I am male.