You hear a lot of things about draft stock this time of year. That player's stock is rising, this player's stock is falling - and in many cases they're rising and falling not because of something new they did, but because of something the media figured out. When the media figured out there were rumors of drug use by Ryan Mallett, his draft stock plummeted - in the eyes of the media.
But that's not a realistic view of draft stock. That information isn't new to teams, and teams determine actual draft stock. Outside of team buildings no one knows where each team has each player rated. That's why you'll see some players seemingly inexplicably fall or rise on draft day: teams know things the media don't. The rising and falling of draft stock prior to the draft is often nothing more than players rising and falling in the eyes of journalists, not in the eyes of teams. There are always surprises on draft day, and I'm sure we'll see a lot of them. Just keep in mind that what may be a surprise for you, likely isn't a surprise for teams.