a metaphor

It still surprises me sometimes at how quickly moods can change.. mine in particular. It seems that I'm having a hormonal imbalance. One moment I'm ok, in a sense, the next moment I shift into a melancholic state. What's up with these sudden shifts? I can't control any of them. They just happen when they happen, and disappear just as fast - that is, when they do go away. This is becoming very stressful for me, much more so than school. It stresses me that I have no idea when the next shift will be, or how often it occurs, or for how long. I just know that it will happen. It's like riding a rollercoaster blindfolded. You can feel it pulling you up, and you know that you'll be going down sometime.. but you just can't hold your breath because you have no idea when the drop will be, nor what will happen after that.. a long ride, a short one, full of twists or very mild - you just can't tell.. happiness and sadness intertwined.. that's life. They're two sides of the same coin.. and sometimes.. sometimes I begin to think that I'd just rather not have the coin..