My cat's acting wierd

So a bit ago my cat appeared out of one of her hiding places and ever since then she's been behaving scared-ish. I mean when someone walks up to her (with her being in her cat tree) her pupils widen extremely. When I do it she relaxes once she realizes it's me, so I know she isn't terrified of me. I'd just like to know what's up with her. I don't want my cat to feel unsafe or threatened in her home. So what do I do?