This is the field in which I work.
The Equality Act 2010 says you have a disability if you have a physical or mental impairment that has a substantial and long term adverse affect on your ability to do normal day to day tasks.
Long term is something that has lasted 12 months, likely to last 12 months, or for the rest of your life if under 12 months (eg something that fluctuates but will always be there). Diabetes falls into this category. As does other conditions ranging from IBS, dyslexia, ADHD, cancer, HIV, depression, endometrosis etc.
Its a very broad definition. Its also a LEGAL definition not a medical one, that's where a lot of people slip up - OH and GPs will only tell you if you are likely to meet the legal definition, they won't say you definitely do. Think about Covid 19 and mask exemption rules - so many places got taken to court for imposing these rules. Why? Cause only a court can confirm someone meets the definition!
Normal can be anything from writing this post on mumsnet - some people might find typing hard due to eg athritis. Travelling to work - someone who is anaemic might feel dizzy and be at risk of crashes or fainting. Someone with diabetes might have to take more breaks than is "normal" etc
Disability can affect everyone differently, even with the same condition, and its not our impairments that disable us, its society - inaccessible environments (stairs no ramps), blanket work policies (we always do it this way), negative attitudes (you're only disabled if you use a wheelchair or if I can SEE your disability). Remove the barriers and the impairment is still there, but we aren't BEING disabled.