This is what I believe is causing this:
Usually sleep disorders like sleep apnea, narcolepsy or anything that causes poor quality sleep, like shift work/circadian clock disruption, restless leg, certain medications, excessive caffeine/alcohol consumption, or just not enough sleep.
Identifying the cause and eliminating it, should help correct your problem.
Hope this helps.
You need to chart your sleeping pattern for 2 wks. This will indicate your normal sleep patter which changes as we get older. It should also indicate under specific circumstances. So you can eliminate external stress. But if the stress level is coming from the same source, it is something that you will need to address and resolve. Remember that part of dieting includes a healthy amount of sleep. This allows you to resume a healthy alert status during waking hours. I found that taking a 1/2 to 1 hr nap between 1 and 2 works for me, only because I still can not sleep 8 hrs. So in my case I treat it like a client. I sleep no more then 40 min. if I'm away from home to give me 15-20 minutes to retouch my make up, brush my teeth, etc.. and back to work. If I am at home I take the full hour. Next. I turn off the cell phone or reg. phones. I call it my "Me Time".
Regarding the external "Stress", I don't let things go beyond two days. No matter what the issue is, I make a decision. Same with the mail, you get it and don't leave it laying around. Either trash it, shred it or deal with it. That you also do with life.
The fact that you are falling asleep while you are driving in most part is because you are finally still in one place and your body is relaxing. I know this doesn't make sense, but if your stuck in traffic you are stuck. You can either get upset or deal with it and reality is that we have no choice then to deal with it, therefore, we get comfortable and wait. Similar to getting comfortable for your nap. Also if it is hot, it's normal to get sleeping just as when you have had a heavy meal.
To keep you awake: Keep a bottle of water while you are driving and take a small gulp. Do not drink it first, but swish it from side to side and then drink it. The sensation will keep you awake and alert. Works during the day and night.
FYI part of a google search on Sleep while driving :
Please search more. These are just FYI. The suggestions above sounds promising...
Sleep disorder 3: Narcolepsy
Narcolepsy is a sleep disorder that involves excessive, uncontrollable daytime sleepiness. It is caused by a dysfunction of the brain mechanism that controls sleeping and waking. If you have narcolepsy, you may have “sleep attacks” while in the middle of talking, working, or even driving.
Common signs and symptoms of narcolepsy include:
Seeing or hearing things when you’re drowsy or starting to dream before you’re fully asleep
Suddenly feeling weak or losing control of your muscles when you’re laughing, angry, or experiencing other strong emotions
Dreaming right away after going to sleep or having intense dreams
Feeling paralyzed and unable to move when you’re waking up or dozing off
Circadian rhythm sleep disorders
We all have an internal biological clock that regulates our 24-hour sleep-wake cycle, also known as our circadian rhythms. Light is the primary cue that influences circadian rhythms. When the sun comes up in the morning, the brain tells the body that it’s time to wake up. At night, when there is less light, your brain triggers the release of melatonin, a hormone that makes you sleepy.
When your circadian rhythms are disrupted or thrown off, you may feel groggy, disoriented, and sleepy at inconvenient times. Circadian rhythms have been linked to a variety or sleeping problems and sleep disorders, including insomnia, jet lag, and shift work sleep difficulties. Abnormal circadian rhythms have also been implicated in depression, bipolar disorder, and seasonal affective disorder (the winter blues).