Depends.
For some, 6 before bed is perfect when they are stable, and if they're not prone to nighttime hypos.
Others are seeing wildly fluctuating levels during the night, and for them 6 might be a tad on the low side.
Like most things with diabetes it’s a bit of trial and error try eating toast and if it affects blood sugar in a high form don’t do it again without insulin , in my opinion of myself I’ve been a guinea pig since I’ve had diabetes , there are rules but they have to be adjustable as one rule doesn’t fit all in the individual world of diabetes
If my BG is 6, I think that is okay. If I am in any doubt, I would not have bread as that would be high glycaemic for me, but what I do enjoy is a couple of squares of dark chocolate. That tends to do the trick as it not only brings my BG up, but does it slowly AND I think it is delicious!!
If you're prone to hypo at night, it's a good idea. I can't sleep if my blood sugar is too low and I toss and turn so much when that's happening that I wake up. I almost never take my blood measurement then (no amount of reasoning when I'm in those states has any effect) so I eat an apple or the equivalent and then in 20 minutes I'm relaxed and can sleep. To avoid this I often have something but not too much (without any rapid insulin) before I go to sleep in the first place - then I won't go too low.
I personally wouldn't eat anything before bed but I do get a bit worried if it's a bit low , A couple of nights ago before bed I was 3.6 so had half a mini twix bar which is about 7 carbs and woke the next morning to a high of 11 so I would probably have been ok to leave it , It is a case of trial and error , lets just hope you don't have too many errors .
Before bed I would ensure that it is at least 4 hours before your last bolus.
If you dip low at a reading of 6 it is either because you've done a bout of vigorous exercise recently or still have active insulin on board . There are other possibilities around impaired digestion but I'd start with these 2 basics.
In that case the toast may help correct a downhill slide of your bgs, but then I'd be making sure my bolus matched up to what I was eating rather than have to snack at bedtime (fattening and crumbs get on the sheets)>