@Celeriac, what did the sweets have in them? I think they'd need to be pretty high carb (and the digestible variety rather than the un-digestible sugar alcohol, polyol variety) to really knock and keep you out of ketosis. Have you got any way of testing for ketones to confirm that this has happened? If not get thee to a chemists and get a pack of Ketostix. They're not ideal as they can also
not show any ketones if you're well into ketosis and no longer disposing of surplus ones, but may be a guide.
The best advice I can give is to go very low carb - i.e. max 20g carbs a day (from veggies) and maybe extra fat for a while to be sure you are in ketosis again. Essentially you need to be sure that there are few enough carbs in your body to make it switch (back) to fat burning mode. It's quite possible to go in and out of ketosis over short periods (e.g, over the course of a day) , and you body can also be doing this without a low carb diet and without people necessarily knowing about it - it's a natural process. This switching in and out can happen even if you're well into ketosis, aka "keto adapted", so as a result
shouldn't cause any side effects - your body already knows how to do this.
I've seen this happening, and my ketone levels certainly can go up and sometimes right down to apparently none, depending on what I've eaten, when I last ate, and what my activity level's been, etc.
I've never come across anything about requiring water to get you (back) into ketosis, so can't help you with that. But you certainly
do need plenty of water, and possbily extra minerals (e.g. salt, potassium) on all low carb diets to replace those you've possibly lost as your kidneys are flushing stuff out at a faster rate.
Robbity