Being cold is a sign that your metabolism is crashing. Your cortisol is probably elevated, which is what was keeping your energy levels high...at least for a little while. If you continue to restrict carbs, you will most likely begin to gain weight back, and experience sleep issues, and get sick more often. Adrenal fatigue will take its toll on you. Low-carb puts a ton of stress on your system. I would start overfeeding with salty carbs immediately.
"One can only be a perfect physician for oneself alone. " ~ Luigi Cornaro