There’s a difference between actual hot flashes and thermogenic night heat/sweats.
I’m a midlife (50+ years) female who’s had many phases of incredible thermogenesis on keto - but no actual hot flashes. I wrote some past posts here on the thermal subject.
Hot flashes are specific in their symptoms - overwhelming quick heat spikes that cause a sweating face and armpits, raised heartbeat/pulse, and face flush, and only last a minute or two (though some females suffer with dozens per day/night) and can occur throughout the day and night, and be combined (or not) with night sweats (which may last hours). You mentioned you’re getting heat up to your neck, which would indicate thermogenesis, not hot flashes? I’m pretty sure?
Thermogenic radiation usually occurs in the evening for me due to hormone levels at that time (reduced cortisol, for starters) - but I’ve read of others on this forum who have thermic heat during the day, maybe depending on age and sex. It is more frequent and obvious when one has a high intake of MCTs via coconut oil that fuels ketosis/brain function and isn’t metabolized and/or high levels of butyrate being produced in the gut. When I was having lots of thermogenesis, my intake of coconut was 2-4 tablespoons daily - and to this day, if I have a high coconut oil day, I’ll notice increased evening heat, but resistant starch without coconut oil doesn’t have the same effect.
You can still enjoy the benefits of enhanced keto brains/BDNF through feeding the good bacteria with resistant starch (refried white basmati is what I use, in addition to daily veg fiber), or, through eating one piece of high fiber fruit (apple, pear - which Dr. Lustig explains doesn’t get its fructose dumped into the bloodstream due to the fiber, and when it reaches the large intestine feeds the good bacteria, like how RS does). A meal of an apple with good nut butter or a bleu cheese dip or just with good cheese, can be an amazingly easy way to get a meal in.
Since you’ve been keto since last June or longer - you may well do better to increase your metabolic flexibility. “Keto” as the Atkins Inductions Phase of 20g carbs or less was never meant to be a permanent lifestyle for the non-diabetic, not only because it’s hard to sustain in this culture, but also because metabolic flex is health. Atkins Phase II is what everyone who wasn’t diabetic went on to - after a few months and being 100% fat adapted - I think it was 50-60g carbs.
Then there’s the LCHF/keto physicians Mary Dan Eades MD and Michael Eades MD in their classic book Protein Power aimed to help their patients stay on the ‘keto cusp’ after fat adapation - not ‘deep in ketosis’ - and their over 1000 patients who healed obesity and metabolic illness are great proof of that. After the first 2 weeks they moved folks up to around 60-75g total carbs and higher for maintenance.
Stephen Phinney MD & Jeff Volek PhD who are longtime low-carb advocates, advise that fat-adapted non-diabetics may do well at 75g carbs up to 100-150g a day - and maintain fat adapted physiology.
Definitely - if you’re feeling like the body recomp is too much/too fast, slow it down! Comfort yourself with more salt & magnesium for electrolytic power, more non-refined carbs as well as making sure you’re eating 2-3 low carb meals a day. Meal frequency calms cortisol (as does supplementation with adaptogenics like dry Ginger). If you’re dealing with high cortisol (from emotional/mental stress and also from intense weight lifting) you’ll find that more unrefined carbs or even a RS routine will be calming and stabilizing