I woke up to hear my dog vomiting under the bed. I tried to get him some water but he wouldn't drink or come back to bed; instead, he just stayed by the closed bedroom door looking to get out. When the door was opened, he went into the bathroom and jumped into the bathtub. When I went to investigate I saw a drop of blood in the tub. I have no idea where it came from on him, but I know for sure it was from the dog. He kept tail tucked for a while and even licked at his rectal area. After about 10 minutes he was back to his normal self and ready to play. What could have happened?