While I don't know for sure what type of "other work" SSDI is referring to (since they never seem to indicate), I do know of people who are disabled and do things like editing books for publishing companies. It is done mostly around your schedule (there are deadlines but you can work for one hour at a time or six) and can usually be done from home so you can sit in a recliner or lay in bed if needed. I don't personally know the requirements for a job like that (if any degree or special training is required), but that is what a lot of people I know have done.