If it wasn't happening before and you didn't do something like sleep funny or lift something too heavy, it's probably anxiety. Do know that if you have neck problems you can have pinched nerves that you might feel in your arms. But you pretty much know when you have neck problems because it hurts, so again, if it didn't hurt before your scare, then it's probably you ginning up fear. It's not caused by HIV, because you wouldn't be feeling anything this quickly. And, if you're like most people who post here, you probably don't actually have much of a risk of HIV, but you don't say. When folks come on the anxiety forum with HIV problems, it's usually not from anything that can actually cause it, but again, you didn't say. Life is full of trials, it helps if you learn to relax more, though that's easier said than done for some people. There's also a difference between anxiety, which is usually not from a known source when it's a mental illness, and being shaken up by something that happens. It can become anxiety if it sticks around a long time, though. It can also be anxiety if, as again is usually the case on this forum, you really have no real danger of having it.