Quick answer
How do you know if someone has put a spell on you?
There is no single symptom. What gives a spell away is things turning up on your path that make no sense given who you are and how you live. People describe it in different ways. Some call it glitches in the matrix. Others describe a feeling of being watched.
The most reliable check is a simple question. What is happening to me right now that does not fit who I am? It might be a run of events, a change in how you behave, or a pull toward something or someone you would never normally choose. When the answer is clear and you cannot explain it, pay attention.
If something fits that description, read can a spell be reversed before trying to fix it yourself, and avoid answering it with another spell from the internet. The consultant can look at it directly in a consultation.
Questions
Is feeling watched a sign of a spell?
It can be. A persistent feeling of being watched is one of the ways people notice something working on them.
What should I do if I think someone has put a spell on me?
Avoid fighting it with another spell from the internet. A spell can be reversed, but that means understanding the whole chain that created it.