Not getting enough sleep at night can cause you to get high blood pressure, heart failure, diabetes, and heart attacks as well as strokes.
If you don't get enough sleep at night you also become less alert, and your reaction time slows and you're not able to think clearly about things.
When we sleep we basically are recharging the batteries in our bodies and not getting enough sleep doesn't allow our bodies to recharge and heal itself.
Not getting enough sleep at night also increases your chance of getting into a car accident which could be potentially fatal as well.