Anyone feel like they're on top of the world, then for no reason feel like the tables got turned?

It's really weird that just 2 days ago i was really happy setting goals for myself (practically unattainable goals) I had more energy than usual I was joking around laughing all day, and feeling very optimistic about my life. Now I feel like I hit a new low.. I feel so alone and like I can't get any lower. This always happens to me and I have the tendency to think self destructively. I think of different ways to kill myself and wonder if anyone would care. I never act on my thoughts though, as I don't have the right to take Anyone's life, including my own.. I try to sit down relax and think of all the good in my life but as soon as I do all the negativity outweighs it, I know I shouldn't complain because Others have it worse but I can't help feeling so worthless. Has anyone ever felt this way or know why such a drastic transition takes place?