I feel like the fitness is going to fall away
It won't in the immediate future.
Personal experience... I'm a few weeks post EfGB first 2 I was fucked no thoughts of running. Last Sat I ran for 20mins and it was great but a dodgy curry that night fucked me over again 2 days in bed/bathroom no food etc so I binned off the week and am starting back with club run tomorrow. It might still be too soon. I'm missing Sale Sizzler #1 on Thurs as it'd be silly to race off the above.
I defo had a point later last week where it felt my body was in full "repair" mode as everything ached, esp my legs.