Random HR meeting, no information on why the meeting was called

My job is changing so this could be related to that, but I got a call last week from my manager saying HR wanted to meet with me and her. It's probably about my soon to switch title and pay, but the last minute nature of it and the unknown factor are literally driving me insane. I feel this constant impending doom and I am convinced I am going to be fired although I have no idea why.

#help.

UPDATE: investigation into policy for accessing protected data. Yay. But not fired, or in jail yet.