I have a chronic illness
I feel terrible making plans and then backing out but I hate never being able to say "Yes, I can/will go" it feels really bad and non-committal.
I want to be a good friend, I want to hang out, I want to be there but unless you call/text/come over and invite me in the moment.
I will never be able to give you a definitive answer. Pain, fatigue, migraines, weakness issues, these are all unfortunately really unpredictable.