Have you ever walked out on a job that you had for a long time?

I'm not talking about some job you had for 3 days or even 2 months. I mean a place you have worked for years.   Say just one day, just saying "screw it" .     What caused it to happen?

I work in a warehouse and have for a number of years. I just cant take it anymore, i've been diagnosed with social anxiety disorder and have aspergers.   I feel stressed out and sick everyday.  Idiot co-workers and no support from management.  Constantly changing assignments on a whim with no warning. 

My one boss is always in a nasty mood and its just a bad environment.  The company I worked for merged with another a couple years ago and its just gone to hell in a handbasket.  It seems unwise to leave but I am just so tired and miserable.  I've tried to make it work, I've felt this way for a good couple years now but just have not been able to have the courage to leave.

Not sure how long it would take to replace this job.  I'm at my wits end.