You know I've read so many posts on here about not being able to achieve todays work-out or this weeks. Due to many reasons, feeling tired, out of breathe and so on.
I can't stress enough how important it is to fuel your body and your muscles. If you don't eat your body is not going to make eat and you'll end up stressing yourself out because you think you've failed. You haven't failed at all, stay positive it's all possible.
I find myself eating at least one hour prior to starting to give myself some energy, eat some fruit as well to give you some slow release carbs which will help. Also drink plenty of water.
Just remember your car needs fuel to drive it, your body is the same.