The lowest bf I have gotten down to was 6%. I agree that it is all about diet. Dont get me wrong I used some clen and ECA, but unless you diet correctly all the T3 and clen in the world wont get you down to that low bf. And ya I felt like shit most of the time, light headed, pale, and did not sleep much. This was my diet.
1600cals at most, 240grms of protein, 140carbs, 15grms of fat. Cardio was 1hour 4days a week, where I burned between 800-1000cals. Another major thing I hate about leaning out to that extent is I found that my strength went down drastically.