Not Cathe, but for what it's worth I thought I'd mention your diet -- I find that I feel a lot more tired by my workouts if I'm not getting enough nutrition. Since you're pushing harder than normal, maybe you need to increase fluid intake too. Or get a bit more rest. I don't think it's necessarily a bad thing to feel more worn out since you're working harder. Just make sure you're taking good care of yourself. And if it doesn't improve after a while, then maybe you should consider backing off a bit.