I was on that flight in row 1 of First.
About an hour into the flight the first officer fell ill. One of the pax was a doctor and saw to him at the forward FA jump seats with two FAs helping and guarding, while the flight continued to MCO. Around BHM, the doctor decided the FO needed additional care and ordered the flight to divert.
Upon landing at ATL the flight was met by an ambulance.
We did get a replacement FO from the SEA-ATL flight as that pilot only had 4 of 15 hours. When we landed in MCO, the FO was to be flown back to ATL.
According to the Captain, OPS organized the backup pilot and he volunteered.
The crew did an incredible job.