Be careful with that... especially in something small like a Mustang. I was coming home from a 19 hour work day back in November and I fell asleep on my way home, running my Yukon into the side of an 18-Wheeler.
Ironically, the next week my boss decided to send me to Atlanta and back (11 hours there, 11 hours back) in his personal Escalade with a 2 hour nap.
But all in all, it really just depends on how easily you fall asleep. My accident happened 3 miles from my exit and cost over $6000 in damage. Stay alert and take frequent breaks!
2014 Ford Mustang 3.7l V6 - 15,000M
2006 GMC Yukon 4.8l V8 - 170,000M
2000 Nissan Altima 2.4l I4 - 279,000M
2002 Ford Mustang 3.8l V6 - 180,000M -sold