Hi Doc,
Too low would be an issue if you use medication to control diabetes (especially type 1) as this may cause a hypo in the night, but personally I would be horrified going to bed with a bg of 8 (I never have a bg level of 8 at any time day or night), but that's me personally. I usually go to bed in the mid 5's, anything lower and I would eat an oatcake with cheese. I have tried going to bed in the 4's but all that happens is that I wake up in the 6's (think I get a liver dump somewhere in the early hours because I have run out of fuel).
Caitycakes x