I'm no expert but let me give this a shot lol. Ketosis simply means that our bodies are using fat for energy. When you're not eating the body will go straight to the fat reserves for its source of energy since it's not getting any energy from glucose (type of Sugar taken from the foods we eat) so it is necessary to be in ketosis stage when fasting. Ketosis is a sign of fat being burned for energy. That usually kicks in on the 3rd day/takes anywhere from 3 to 5 days to see appetite suppression but can happen sooner or later; really depends on the person. Hope that was a bit helpful. Take care :-)

You will be in ketosis as long as you eat fewer than about 50 grams of carbs per day. That's generally the number people use to designate the line between ketosis/not ketosis. For some it might be 30, for some it could be upwards of 80-100. It just depends.

If you have ever been low carb in your life, you know that drifting in and out of ketosis is very natural. Low carb people tend to get back into ketosis faster than the carby folks. I've been low carb for years and after getting carby for a couple of days, my ketosis kicks in at about day 2.

Ketogenic diets are used in children with epilepsy. We now have a couple of studies indicating a ketogenic diet can help people with brain cancer in terms of shrinking the cells. See Seyfried, et. al.

There have been a few studies indicating that ketosis can cause heart palpitations which are the result of increased uptakes of norepinephrine, adrenaline and cortisol.

If you don't have a history of heart problems you should be okay but check with your doctor if you have any concerns.