Late-Night Mistakes at Work

Last night, something weird happened on my shift. I was so tired from working all day and into the night that I accidentally left a memo about today's sales numbers open for anyone to see. I walked out of the room without realizing it until hours later when I noticed someone else had read it. Now everyone probably thinks I'm sloppy or forgetful, but what if they think worse? That I don't take my job seriously? Should I just pretend nothing happened and hope no one said anything to our boss? Or should I confess and risk looking bad? I feel so silly for making such a rookie mistake. Has anyone else ever done this? How did you handle it?