It's called Boon of the Spirit and it's a scripted event when you fight dark Revan. Besides that, Revan's spirit is doing multiple things such as telekinetically lifting parts of the temple. There are also a few character statements during the fight that refer to a 'presence'.
That's besides what dark Revan was doing. Whilst the likes of Krayt and Plagueis have fought through organ failure and such, Revan was literally willing himself to live and performed everything he did whilst warding off actual physical death. He was arguably invincible and only stopped when his Force reserves were exhausted.
Originally posted by ILS
Sounds like game mechanics fam, but feel free to post links and screenshots to real evidence whenever.