Can't stay awake after lifting.

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Whenever I lift, I fall asleep after. My usual workout is jogging a mile, and an hour or so of lifting with breaks between sets. I'm trying to lower my body fat percentage and increase my muscle mass. I then go home, eat a sandwich or something and drink a protein shake. I then fall asleep doing homework or something. This happens every time I go to the gym. Could this be caused by diet? Do I need to increase my protein or carb intake?

Thanks for the help