you are covered under the Disability Discrimination act and have the right to be treated on an even level with other staff. However they really do have to have in place guidleines to assist you and keep you safe within the working environment. Maybe a disemination of information about the illness to other employees would assist in catching the warning signs.
I think the problem comes, with those diabetics who are completey uncrontrolled, have no interest in helping themselves or attempt to control the condition, and then use it as a tool for sickness.