The disease is indeed treatable, especially in an early stage like this. Stimulants, exercise, forced sustained activity and good nutrition will beat it back entirely. A taste of this can be shaken off like a mild depression.

The issue is that this is not simply a disease; it is also a contaminant. The disease would run its course naturally if the subject simply did not return to the depths of the facility. If he goes back in and is exposed further to the displays then it will progress regardless of countermeasures. Extended exposure will render him like unto these Mechancius adepts: unable to summon the will to move even as they are executed by servitors. 

One other detail - this particular lethargy is location-bound to this particular facility, to this particular Scribe. All of the Lords of the Garden have concocted a unique desolation, and the plague that laid the Jade Tigers low was not the same as the one that ravaged the Children of the Omnissiah. Futures where you simply leave still involve danger and death, but not this danger and not this death.

*

The challenge before you is thus:

The first of the Scribes is within the depths of a Mechanicus facility. The principle hazard of this facility is the cogitator screens - they are still active, displaying corruptive images, vectors for a lethargic disease. A single glance will not immediately cause debility, but sustained exposure will advance the infection. At issue is that the Mechanicus facility is enormous, with tens of thousands of screens on a vast array of devices.

The second complication is that you are not the first on the scene; Forgeworld Draupnir has deployed a strike team to extract the facility's secrets, and if they terminate the Scribe before you can reach them then a powerful asset for the Warmaster will be lost. Going blindfolded may inure you to the diseased displays, but will render you vulnerable if the slaves of the Omnissiah strike.