Day 12 - Heavy Fatigue - Advice?

I am on day 12 of the MC. So far, I have lost 18 pounds, with 20 pounds being my goal. I plan to stay on the cleanse for 21 days for the health benefits.

The last day or two, I noticed I am getting very fatigued throughout the day. Yesterday afternoon I merely cut the grass and it felt like I ran the entire Boston marathon. I am exercising as usual and am very active and fit. So this type of fatigue is extremely unusual for me. I even went to bed early last night and slept 3 hours later than usual. I am listening to my body and giving it the rest it needs, but this is not my norm.

Is anyone else experiencing this or have any advice/tips on dealing with this?

Raymond