I feel exactly the same, a bit run down. But not on glicazides.
My levels are around 8-10 before meals and shoot up to 12-14 depending what I've eaten.
I ride every other weekend on my mountain bike x country for 2-3hours. It seems as my levels get closer to the recommended 4-7. It takes longer to recover after excercise.
This may be why your MODY. It is a different classification to "type 2". You don't fit the standard profile, nor I, so you may need to see a MODY specialist.
I can only guess, maybe if your getting readings of 4/5 after 2 hours of food consumption and with glicazides. It maybe to low a reading for you. I always felt sick going that low. I function better on the upper end 6-8. But thats me. Its your body and it tells you how it feels.
What dosage is it? Can you change it?
Obviously the insulin is blocking the nutrients getting to your blood, hence the tiredness.
As for your weekend, maybe go for a long stroll after dinner or plan somethink active after the meal to burn off the indulgence. Try everything you like, but have a smaller portion. I wouldn't stress, I have a guilty pleasure now and again, but balance it out with excercise to get my levels down.
Don't beat yourself up if you fall of the wagon now and again, think of it as a reward for all the hard work you put in so far, your in control and you've done really well by the sounds of things ie good levels 4/5.
Stay focused on the positives, try not to dwell on the 'what if this or that'. Address every situation as it arises. Everyday will be diferent, we all have our ups and downs. Thats the rollercoaster of life.
I have my annual check up soon, so I will find out more about MODY.
Enjoy your weekend.