First dose of Tirz.

I just took my first 0.5 dose and I’m honestly freaking out a bit. Within a short time I got really anxious, like a rush of nervous energy I’ve never felt before. My skin started itching which made me panic more, and now I’m stuck in this loop of “is this a reaction or is this just anxiety?” I’ve had to log off work and go for a walk because I couldn’t sit still. I even took an antihistamine just in case, but my brain is still running wild. I know 0.5 isn’t a high dose and I did that intentionally because I was nervous to start, but now I’m second guessing everything and worrying I’ve done something wrong. Has anyone else had this kind of reaction on their first dose? Did it pass quickly? Just looking for a bit of reassurance because this feeling is pretty overwhelming right now