Well if you weren't eating many carbs to begin with, it sounds like you did a gradual transition that lasted more than a month. Since you had no negative symptoms, that would put you in the "more than a month - no" category.

A rapid transition would be going from eating moderate to high carbs to eating very few or none in less than a week. The poll is trying to determine what factors might minimize the negative symptoms of ketosis that some experience. It seems like the faster the transition and the more dramatic the change, the more likelihood there will be ketosis symptoms as the body tries to rapidly change over to using fats as fuel.

I think you have to define transition in a more narrow sense. I think you will find, especially as the person gets older, is that the complete transitioning effects of the diet will take place over a number of years.

Thanks for the input, but for the purposes of this poll, I'm not getting into side effects that disappear years later or don't appear until years later. If you want to make that poll, you are welcome to. I'm mainly focusing on the things that make people quit ZC or carnivore or VLC within the first month or so. Most people don't seem to want to wait years for problems to disappear, and I can't blame them.

I tend to agree with a poster above that if you do want to eat vegetation its best to do it in the summer time.

Yes, me too. One reason is that carbs seem to make me feel colder, whereas fats tend to have the opposite effect. Though, strangely, fats don't seem to make me overhot on hot days, even though they help me feel warmer on cold days--I don't understand that one. I think Lex touched on this, maybe he can explain it. Even among SAD dieters there is a folk tradition of eating bone marrow soups in the winter to warm up. I used to think it was just because of the hot temperature of the soup, but now I suspect that the fat is another element in the warming.

The reason why I tried diet was because of severe cystic acne, which began clearing straight away. I didn't notice any side effects because I wasn't looking or focusing on them, the mirror was my guide. IMO many people probably imagine side effects to some degree. What should I even have been looking out for? What does 'feeling bad' mean? When I ate a typical teenager diet I never felt 'bad' and was very rarely sick as in being confined to a bed but despite this obviously had some severe health issues.

I had been eating lower carb due to numerous food allergies for a couple years (I'm also convinced there was/is a fairly well rooted Candida issue).
At some point I switched to a fairly pure meat diet (chicken thighs usually with the occasional beef). I never had a chance to start burning ketones though as the calorie content from fat of my meals was probably only 50% and there were almost weekly indulgements in one carb or another in attempts to find something my body would/could handle.
I switched to all meat (cooked rare/bleu) a month ago and have eaten everything rare for close to two weeks now.

Even on my stepped transition as it were (I don't know if you could call it cold turkey as I was mostly low carb before this last step) I've still had some problems.
At first I was mentally alert and had lots of energy. Over the next few days my energy levels began to fall followed by 2-3 days of mental fogginess and attention issues. I've only now begun to start feeling "right" and I can tell I will feel even better over the next week or two. My daily morning jogs went from ~10min/miles to 6 or 7min/miles, to 10 or 12 min/miles, back to 8min/miles this morning. I even missed Monday morning because I felt like someone beat me with a bat overnight. Once I get warmed up though my endurance has been getting better the whole time.
The only stomach problems I've encountered were loose stools in the beginning from eating lots of fat. I got nausea as well. I'm tolerating it much better now. I got this from both raw suet & marrow as well as marrow bones warmed up in the oven or on the grill (first couple weeks). This too seems to be clearing up this week.
No issues with my teeth but my breath is rough (ketones I assume, I can smell the change in my urine as well).
I had been a bit more easily aggravated for a week or two but now seem to be fine (if not a bit more mellow). No paranoia or anxiety.

It was very easy for me. I went from VVLC vegetarian (under 20gm. carb / day) to ZC. I love it. No problems at all. Energy is fantastic, particularly since doing raw ZC.  Since doing raw ZC plus Warrior Diet (one large nightly meal), I have gotten leaner in the abdominals / waist and put on more muscle. I could not be happier.