I have done Keto for a year now. Recently have become very committed to recording blood glucose levels, and it has been immensely helpful in tweaking what I eat. I have been humming along nicely for several days with my blood glucose in the low 70s. For some stupid reason, I ate a donut this morning. I feel sweaty, anxious, unsettled, and my heart is beating rapidly. It was too sweet and did not taste nearly as good as I imagined. It doubled my blood glucose to 144. This is a real learning experience. I wrote all these reactions down so I can refresh my memory before I engage in stupidity again. 
I think for the first time I truly understand that this stuff is poison, and I have been low carb long enough now so I can hear my body scream at me when I subject it to such.
Remembering mistakes so as not to repeat them
I have had similar reactions anytime I decide that “cheating” is a good idea. I get heart palpitations, hot and sweaty and sometimes headachy. This is especially if I choose to eat a dessert of some sort. I have been binge-listening to 2 Keto Dudes and this morning I heard the episode “Mad as Hell”. I really think that before starting Keto that I was becoming diabetic. On paper my blood sugar was okay, but anytime I ate sweets I would feel immensely bad. Especially if I eat sweets in the morning. I have been committed for a while now to no cheating. I feel much better not cheating. I feel good. I am beginning to see sugar as poison. I just wish I could convince my family. It is really hard to get everyone on board with this way of eating. I have been Keto since August of 2016. I have lost 30 pounds with about 20 to go.
I also found that when I expected a luscuous sweet cheat treat, it invariably had a drying edgy unsatisfying effect which led to cravings. Being in keto is definitely the more pleasant calm comfortable state to be in. Also a slight feeling of hunger that used to be the warning of impending sugar crash with its pains and loss of ability to concentrate, is really now a prolonged pleasant state of alertness to remain in.
That became one of my stock phrases too. Sugar is poison.
I had a reaction like that to cookies at Christmas. First my BG plummeted and then went up. I believe they call what happened to me reactive hypoglycemia. If I only have a bite of a sweet it doesn’t happen.