I wouldn't say they are dangerous. Diet of course has a lot to do with levels, so if they are in the range you stated for 5 hrs then I'd be trying to lower them some. It's all trial and error. And it can be difficult, I find keto works for me. I do take insulin, but it keeps the requirement low. I also find eating to a pattern reproduces more predictable results than just eating differently at each meal. And what I mean by that is you can chop and change what you eat, but keeping the macros about the same helps with getting results that are more predictable and makes life easier I find.
Personally, I try to really avoid numbers in the 8's.... but that is a standard I set for myself. Not something you should do, what works for one, doesn't for another, so you will learn things as you go and work out your own plan.