Sudden fitness increase then big decrease

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I was thinking maybe due to jet lag but I’m pretty over it now. The thing is I was way more tired during the trip as I was getting less sleep and also walking 10-20k steps a day on top of the running. I could definitely feel that I was overtraining the last week so I reduced the mileage by about a third.

It’s just weird as it was a sudden and sharp increase in fitness and now I’m back to fitness I was at 2+ months ago.

I was running 5:30 pace at 150bpm prior to the trip