I've found that sometimes it's not always the fact that your getting weaker or run down, you may just feel that way briefly until your body adjusts to a new routine or diet. Any time you change your caloric intake or workout volume your body needs to adapt, so just because you feel run down for a couple days does not mean you have to go changing things drastically. Stick to it, let your body adjust, and you'll be much happier with your results. I find this easier to cope with by additional caffiene intake and making sure to take plenty of amino acids to help keep my strength. SS tip 101