I think I have some sort of mental disorder?

i think i have some kind of mental disorder. for about the past year ive been having very weird modes every week or so where i feel kind of depressed but its a lot deeper than that, i start to think about where my life is going and how much i ****** things up, . i just start to look at the bigger picture with everything. its really hard to explain, i feel like i shouldnt be alive or i should commit suicide and i worry that im not like other people, they dont think like i do and just move through life but i dont think i could ever handle doing anything serious. im a very very insecure person and always have been, i feel like no one will ever understand me and that maybe it would be better if i just wasnt alive. why is noone else just looking at what the world is like and why people work the way they do? often when watching things like fantasia i get deep into this mode.