Feeling Distracted at Work...

I've been having one of those weeks where everything seems to slip through my fingers. I forget meetings, misplace files, and I just can't concentrate. Today, I even hit reply all on an email asking for help with a project when it was meant to be about personal leave arrangements.... It's not like me at all to make such careless mistakes. Is this normal? Do you ever have weeks where everything goes wrong and you're left wondering what happened...?