It's not coolest but just applying common sense.
Why Oda needs to show Grim Reaper just to highlight hallucinations?
We already were aware that Zoro will face Backlash after the medicine so why Oda went a step forward to show Grim Reaper that too when Zoro is actually awake??
There was absolutely no need for Oda to show Grim Reaper just to portray an effect of a medicine.
Does this make sense to you from narrative point of view?
No
It's not hallucinations.
And, visible wano spirit has no basis here.
But Enma - death sword/demon sword - Zoro named attacks after Demons/Hell - Zoro being king of hell - Asura - And, Now Grim reaper
This connects very clearly and logically.
I am reading between the lines. Not my fault if everything about Zoro ends up being cool lol
Why does Oda do anything in his manga?
Why have Yamato go on a 10 chapter side plot for Kid/Law to resolve the Kazenbo plot for her?
Why have Sanji claim he'd take out Page 1 when he didn't?
Why have Sanji claim he'd stop Big Mom with his cake when he didnt?
Why have Jack get up only to get offscreened and 1 shot by Inu?
I could say these things for a 1000 other reasons. The 2 reasons i gave you for Zoro are literally reasons for him to do so.