“Prophecy” is episode twenty one of season six of Stargate SG-1.
SG-1 is visiting a planet where the Goa’uld System Lord Ba’al is the god. Although SG-1 believes that Ba’al has abandoned the planet, a Goa’uld emissary still visits the planet to collect any naquadah that has been mined, claiming to be taking it on Ba’al’s behalf. Whilst they are meeting with the locals, Jonas passes out. In the episode “Metamorphosis”, Jonas was subjected to experimentation by the Goa’uld Nirrti as she strove to create a Hok’tar.
Jonas has started seeing visions of the future – although the others are sceptical to start with – but according to scans he has a tumour which is going to kill him.
The problem is with interpreting the visions as to what they mean. Attempts to change the outcomes of events seem to be actually causing them.
The tumour needs removing before it gets too large to do so safely, but Jonas’ visions show something really bad is going to happen.