Do i need stress leave?

i must start by saying i love the work i do but my employers are the root of the problem.i am a plumber for a national company and over the last year there have been many policy changes.now i am very experienced and knowledgeable. And also have great re pore with my customers but in recent months the jobs that have been coming in have been going to less qualified plumbers(i know this because my company will send me out to fix the problems they cause) so of course this has had a profound effect on the am out of money i bring into the company and now they have been threatening to terminate my employment due to my performance(even tho i have had no disciplinary actions or problems with customers. this has stemed back to when i told a supervisor that i do not want to make money dishonestly as i have seen many unessecary repairs and replacements. so in short i have been getting the worst jobs that call in while less experienced techs are getting the good calls i was getting at this time last year. so the constand fear of loosing my job in this tough economy has made it to where i dread going to work to the point i am getting headaches and just barley make it through a work day...and did i mention i work on commition so last year at this time i was bringing home an average of 700-1000 a week and now its about 200-500 a week.