how did walter miraculously recover from the poison?!

নমস্কার Moi, I think Walter took the poison in the sewer's and Peter and Olivia got him back to the lab in the 1 ঘন্টা time frame and give him the antidote.
Hope this helps.

If আপনি did not see the end of the episode they went back to the lab and made a antidote that works and cured the poisening

i believe the reason that Walter was not killed দ্বারা the poison was b/c its an inhalation drug. He was only exposed to it for a few moments of time and olivia smashed the beaker that the posion liqued was in so that it could no longer travel the air in its gas form. Walter was taken out in to the fresh air and প্রদত্ত an oxygen treatment দ্বারা paramedics. I believe this is what saved him

আপনি are correct Fringeaddit86 in the প্রদর্শনী they ব্যক্ত that he wasnt expose to the affected air for a long time thats why he got better on শীর্ষ bc he also got an air mask.