Every time I've ever got a new job, whether a different employer, or a promotion, or a sideways move, I've been... unsettled for weeks, even months, afterwards. Feeling loads of pressure, and turning all my feelings inwards on myself, and always feeling like I didn't know what I was doing and whoever had hired me had made a terrible mistake.
I think it's normal. Or at least, common. Because in almost every scenario where you go from one job to another, you were to some extent comfortable in the previous one. You knew the employer and the culture and the unspoken agreements and the tasks and the standards and your colleagues, and even if you had a serious problem with one or more of them, still you knew them.
Then you go into something new and it's like a rug being pulled, and because you don't really have any evidence of you succeeding at the job yet, your brain fills in the gaps that you're a failure and out of your depth and the whole move was a really bad idea. And those ideas swirl around your head and it's worse because you don't properly know anyone well enough to ask them for honest feedback and believe them when they provide it. So you get stuck in an internal feedback loop that's just you thinking, "I should be able to do this, but I'm finding it hard, so maybe I'm not as good as I thought I was, I was so arrogant/naive/reckless to think I could do it..."
And you don't even realise that one of the things that's making it hard is how much of your energy is being taken up with those thoughts.
I often think of every career move I've ever made as a case of jumping off a cliff and working out how to fly on the way down. But the thing is, I've always managed it. It's been scary as hell and definitely multiple moments where I thought I'd ruined everything and was going to plunge down into the sea or crash into the rocks. It's been confusing and frightening and difficult and I've had to work hard to dislodge myself from the thought that I should have just stayed where I was and not tried. But it's always turned out okay.
You took a leap, and maybe the contractors were the parachute, or the safety net, and now they're gone it's a bit more difficult and scary.
But you've got this, I promise.