Get past the wheelchair model of disability access. Just as people who use wheelchairs shouldn't have to go to the back of a building and use a freight elevator, people with invisible disabilities need to be considered when planning buildings, access, and service provision. People with invisible disabilities should have equal access BY DEFAULT, and not have to spend their time constantly educating people about their illness in order to get through the day. Businesses need to do some basic staff training about the variety of invisible disabilities. Consider the whole range of somatic, sensory, and neurological issues and atypicalities, from CFS to cancer to dyslexia to deafness to autism to mental illnesses.

Oh, and don't tell them it's all in their head.