Why didn’t Laurie tell Bracket that someone was following her?

I'm guessing it was because it was Halloween and Bracket probably wouldn't think much of it (unless she told him after the mask, etc was stolen from the store).
But you know how movies are.

Part of her thought it wasn't real either, and she was just going crazy.

back then women were regularly followed and not much was thought of it,
the term is "stalking" these days but back then it was just a man being interested in a female

She wasn't sure whether it was her imagination or not.

I would have too. I never understood why she didn't say anything...

It was halloween. She kept it to herself probably thinking its nothing serious or someone's doing a halloween prank on her.

Edit: besides, she got scared when she bumped to the sheriff, so she probably forgot the whole thing for a brief moment.

Jones70, Laurie isn't sure how to explain the matter. Michael Myers is not a kid playing a prank, the elder pervert of the neighborhood, a clear criminal, or an identifiable mental patient. He doesn't fit in to any category that the police are acquainted with. Laurie senses that she is in danger for a personal reason, but can't present that information because she doesn't know what is behind it.