1. Type 1s are not allowed to eat sugar (because our sugar levels are high)
Blood sugar can go low when too much insulin is injected for what we eat or exercise. Therefore it is not about eating sugar or not, but rather the quantity of sugar (and carbohydrates in general). From personal experience my normal diet does not include a lot of sugar (and generally carbohydrates) because it raises my glucose levels so that often the insulin I have to inject for it doesn't work quickly enough to keep levels relatively stable.
When it comes to training and racing, the amount of sugar/carbohydrates matters most! If I feel my levels are dropping I often use wine gums or similar as well as fruit bars or gels to get my sugar level up but here is the key: I won’t have an entire gel but say half or I eat three sweets rather than 10. This allows me to have just enough sugar on board that my body needs, without going so high that I need to inject insulin to bring levels down again afterwards.
The closest for a healthy athlete to get to experience low blood sugar is when he or she is “bonking’:
This term describes a situation whereby the athlete experiences extreme fatigue and loss of energy which can occur after very long training hours and is caused by the depletion of glycogen stores in the liver and muscles. Usually there are some signs accompanied with this like change of mood or feeling a little dizzy. These are very similar to a Type 1 having a hypo.