Well, hmmm, how about this for a question:

Is it better to stick with the stress you know or the stress you don't know?

You won't have as many bills at your sister's, but you also might not have much privacy and time to yourself when you really need it. Are they going to be receptive and understanding of your moods from day to day? Are they going to expect more from you in household responsibilities than you're presently able to live up to?

Is there any way you could car pool or cut your travel expenses? Is it possible to telecommute part or all of the time? Can you work in split shifts and have a rest area set up in the office somewhere. Will your boss be willing to let you work around your day-to-day symptoms? Work a little more on the days you're up to it, and less on the days you aren't, as long as you put in the required hours each pay period?