Are you eating before you work-out? It's just as important to have food in your system before as well as after the work-out.
What's your heart rate at? Do not use the meter on the treadmill, physically take it yourself. Personally, when I'm overworking it, I get the dizzy spells.
Are you sweating? Start either drinking a propel, or use the Crystal Lite with electrolytes in with your water it'll make a difference.
That's it--my body needs a kick in the you know what to get back into shape!