why is it?

tell me why is it that you can be on the highest mountain one minute and on the deepest valley the next? it's really bazarre.
For instance, my mountain:
I was so thrilled and estatic to find out there is a very large possiblity that I'll be able to work at the school I'm doing practicum at because it seems that they really like me and the resource teacher pretty much flat out told me that she wants me there next year to take the place of a girl that's going to be going to grad school next year. So that was extremely joyful.
Now my valley:
after everything seemed fine, me and my friend are finally on the outs completely after their pyscho girl friend lied and said I did something I didn't do. So now I'm blocked and she's got full control!
Now only that but I feel like total crap and a useless lump whenever I go to youth now. I don't feel like I make any sort of difference there anymore. AND to top it all off my Laptop is completely bunking out!
and yet i feel terrible cus I feel like I'm only focussing in on the bad stuff!
lets go back to my mountain!
I'm extremely thankful for the blessing I've been giving to have the opportunity to work at this school and for the fact that i've heard that they want to keep me!
I'm just praying that i don't have my hopes suddenly snubbed down... I will be heart broken!
Who knows what this week will bring. I'm praying that I don't have a mental breakdown!