Ok so i have a problem with prescription medications that got really bad about 2 weeks ago....?

i ended up losing my job because i called in sick too many times and my boss asked for a doctors slip the last time. i obviously wouldn't get one because i was faking sick because of the med abuse which caused me to be very groggy and just too messed up for work. since my boss said if i was sick one more time without a doctors excuse he would fire me i decided to stop going to work. And i obviously got fired. Now i am challenged to find a new job because i have a deadline with a high school to find a job or i will not receive a high school diploma. my question is how will i be able to explain to an employer why i lost my last job? p.s. i quit the med abuse.