I found this out yesterday.
Expedited Reinstatement is a way to get back into Cash Benefit Status (start getting your money from Social Security again) if you have to leave work because of the Original Impairment (the disease or condition that caused you to get a Disability Benefit in the first place).
If you have been on a Social Security Disability benefit (SSI and/or SSDI) and you back to work and you do so well that eventually you are no longer eligible for the benefit but then get sick again and have to leave work, you can request an Expedited Reinstatement. Social Security will look at the request and take up to six months to decide whether it is valid.
During that time they should be paying you Provisional Payments (you might have to ask for them).
A provisional payment is a payment of the benefit while they're deciding the request for EXR.
If you had been on SSDI for 24 months (or have received a lump sum retroactive payment equivalent to at least 24 months of payment) you will be eligible for Medicare.
If, however, you request for an EXR is denied, you will LOSE your Medicare.
If, however, instead of requesting an EXR and you file a completely new claim and it is denied you WON'T LOSE your Medicare.