Carrier/rack problems of the 2011 Dodge Avenger

There was an exhaust leak under the driver's seat which caused me (only driver) to become very very sleepy. I was in the car for 5-10 minutes when I felt the sleepiness. I had to open windows for fresh air in order to make it to work (20 min. Drive) without having to pull over. The sleepiness started about 3 weeks before it became really bad. I was on a 4 hour trip & after an hour I had to repeately pull over, one to sleep for about 30 minutes. At the time I did not make a connection with what was happening. I attributed the sleepiness to being tired but after the third day of serious sleepiness, I thought there had to be something with the car because it only happened in the car although there were several days that I was abnormally sleepy at work in the morning hours. I believe that was a carry over from the trip to work each morning. There is a vocational school in the public school system where I work so I took it to the teacher of the mechanic's class. They have a machine that shoots smoke through the exhaust system & there was smoke coming through a crack in the exhaust pipe located directly beneath the driver's seat. I went to the doctor for a blood test to make sure I did not have any carbon monoxide in my system. The results showed me at a level 1, the range is from 0-2. The mechanics repaired the leak with a special puddy. The drive to work everyday is a twenty minute drive each way on a four lane highway. The first incident was April 23, 2016. The other incidents were the week of may 16th. I was exposed to the fumes for about three weeks before it became really bad.