I looked up the Spanish version and the one here seems to be incomplete, there is a couple of panels missing from the end of the chapter. In the missing panels Sung Yeon says he lied about remembering everything because he was worried about Hosik, but a month later he actually remembered everything.
I found it in an earlier comment
https://lectortmo.com/library/manhwa/32780/hosigi-iyagi
I think the part about him collapsing is the last special released, and is not connected to the lost memory arch. The last part where Sung Yeon collapses is a separate side story about another reincarnation of Sung Yeon. At the end of that chapter the author says that she/he wanted to write a sad story and that it will be about 5 chapters. It's called 1950, I'm guessing it's based in that decade.
Here is a link, chapter 94 has the missing panels from the end of the memory loss arc, and chapter 95 is the beginning of another side story set in the 1950s it seems.
https://lectormanga.com/library/manhwa/32780/hosigi-iyagi
Might be a spoiler butt i dunno
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(No confirmed just assuming fromnthe context)
If he was faking this shit for attention from hosik i might actually get a little mad
BUT
i read the raws and by read i mean suffered because i dont speak spanish but from what i gathered i think theres been like an overlap of the timelines for hosik and seungyon or something . Please correct me if im wrong