anger and tears

I don't know if this happens to anyone else, and I just noticed it today, that it happened to me. Today was going to be a good day. I was going to wake up, give blood, go shopping, and have fun with my roommates. Instead, I slept in, got woken up by my brother yelling at the door and did give blood and go shopping. The only problem is, the fun was gone. It's like, only I only have fun shopping, and my roommates just get it over with. Now, we weren't buying anything particularly fun (cutting boards and tolilot paper just aren't that exciting), but I like going to Wal*Mart, just to go and look, and if I get to spend money, well that's part of the fun. The problem came in when I got home. On the way home, one of my roommates mentioned she used my bed and desk to set up her computer/monitor since her desk died this morning at 6 am. I had said that's okay. But, the minute I step into my room, I actually see it, and it registers, and she has her computer, her tablet, and a textbook on my bed, and it sinks it. She actually was sitting on my bed. Now, I normally don't care too much about people using my things (if they ask), but they didn't ask. And I like my bed. A lot. I use it for homework, relaxing, reading, and, of course, sleeping. It's like my personal space in a college world where you get no personal space. So, I mentioned that it would be nice that next time, they should ask. Now, my roommate is paying for her own phone, and she has a cell phone where she pays per minute. She said that it would cost her minutes, which I completely understand. So, I picked up our apartment phone, and said "you could use this". Now, when I said this, I was upset. I felt like someone had invaded my personal privacy, and I realize that I wasn't being fair, but I was asking to be told in future, and just got upset. Things were said that probably neither one of us meant, and I stormed off to my room. I pulled out my laptop, fuming, and opened up iTunes. I was making a new play list, then the next think I knew I was close to tears. I had gone from angry to crying in less time then it took to write this down. Am I the only one this happens too? I don't get mad very often, but when I do, it's not very pretty. And then I burst into tears. Hopefully tonight will be better. Oh. and I moved. and I'm surviving.