Sudden waves of Euphoria - serious question

No, not that sort of euphoric. Anyway, I thought I'd share this odd experience I sometimes get and see if anybody can offer an explanation, or a similar story. It's not bad, per se, just intriguing. So, whenever I anticipate something happening - usually something mundane - that I actually, physically experience, I get a wave of euphoria after it's happened. I can give three examples. The first was years ago when my mate began shaving. He told me he needed to shave, so, for some reason, I accompanied him. After anticipating him shaving, him actually putting the blade to his cheek made me experience this euphoria. The second was at work, when I was putting away the warehouse key. Inside where I put the key was a big pile of what looked like sand or mud. After telling myself that it was a pile of sand, I felt a sense of euphoria as it slipped away beneath my feet. The third is also from work, where I spotted a room in the warehouse which I hadn't before seen - it was a little bathroom. I decided to check it out, and when I flicked the light switch so that I could actually see the room, I felt this wave of euphoria. Any explanations?