sudden feeling of betrayal

How to explain how i can fall from feeling all happy and pleased with myself to feeling quite sad and unsure in just a few minutes. One second i was all happy and feeling good because i managed to get our counterparts to accept changes to budget and content of a project, while also getting praise for my work. Next, I suddenly got the feeling that one of my best friends was making fun of me behind my back. Paranoid? Perhaps. but regretfully i'm not so sure and hence i'm not so sure anymore that this good friend is actually such a good friend. So perhaps the sudden fall of my mood is explicable. Just sorry i could not have been allowed to feel happy for a bit longer for once.