I suppose the answer to the question is no it’s not useless, it just needs adjusting , any sort of infection , virus etc.will cause blood sugars to rise, in my experience anyways , so using same amount of insulin as normal will definitely see rises , and make insulin effectiveness seem “ useless” , I’ve been T1 for over 40 years and I’m still experimenting depending on varying situations, unfortunately that is what living with T1 is all about , it would be so much easier if 1 cap fitted all. But as we know that’s not the case, I hope you recover soon , and on a positive note you now know what to look for should a similar situation arise in the future , and that experience and knowledge is what makes living with diabetes a bit easier .