I was somehow able to hold in all my distress through most of the next day. But then over my pork cutlet dinner, I blurted out to my friends, "Uh...I think there's a ghost in my room!".
They looked at me, and they were all wonderfully calm. We shared ghostly experiences and talked about why the ghost would want to hang out in my room. Maybe the ghost was musing on why I was hanging out in his or her room at that same exact moment.
I went back upstairs, poked my head into the bathroom and introduced myself to the general direction of the sink. Then I gave a light lecture on water conservation, though I added reassuringly that I was actually quite amused by all the trick playing. Finally I respectfully requested that the ghost make her or himself comfortable at anytime in the room, except while I was sleeping.
The tap never turned on by itself after that! And the ghost was great company, we watched many a bad TV show together that week.