I feel anxious after casting a spell. Is

The anxiety reads more like the weight of having done something carefully than like a warning.

One card came up for where you are now: Knight of Pentacles, reversed. Upright this knight is the slow, methodical one — routine, checking, doing it properly. Reversed, that energy turns inward and heavy: the urge to re-check whether you did it right, to sit with the result instead of acting on it. That is the shape most consistent with a feeling like yours after a casting. It is a description of the mood, not a signal from anything.

So: nothing in the reading says something went wrong. If when you lay the cards back out, what was actually on the table matches what you remember — the heaviness is just the reading's own weight, and it will pass. If your memory of the casting doesn't match the record, then the tension is sitting in that gap, and that gap is worth looking at rather than the meaning of any single card.

This turn's step, if you want one: put the cards back out on the table once and write down, before you compare anything, what was actually there — positions, orientations, the question you set it up with.

One thing I don't know and it would change the reading: by "casting a spell" do you mean laying out tarot cards, or a ritual you performed?