I woke up middle of the night to something running down my face.
Turns out I had sun burnt so badly that my forehead had blistered and some of them had burst so I had the juices running down my face.
I went to the back of the plane to get help and one of the flight attendants spent the better part of two hours cheering me up with jokes and stories while I dabbed at my forehead with cool flannels/disinfecting etc.