Fat burning doesn't equal ketosis. Your talking one extreme to another.
Took me about two weeks both times I dropped my carbs. For me, testing my sugars, my body was running too high. Switching to a lower carb diet, my sugars became more normal, not low, just not high. However, my body thoight it was low because it had been used to a high baseline sugar. After a couple weeks of feeling extra hungry, boom, there is suddenly a switch and everything is easy after that. Byebye debilitating lower back pain, constant hunger that doesnt go away even immediatley after a large meal, numb hands, migraines... and fat just slowly melts off.
I agree on watching the electrolytes during the transition and don't keep going back a forth. The transitions are the hardest part on your body.