Normal stuff
You have a specialized set of skills that need to be exercised or they atrophy, what you are describing is likely normal. Professional athletes practice virtually every day of the week during the season; you use skills or you loose skills.
I was out for 7 weeks due to a fairly serious recreational sports injury and was appalled at my performance after returning to the line. By the end of the second 3 or 4 day trip I was back up to speed. Even instructors, who sit giving simulator training day in and day out, feel rusty when they return to the line after being away for weeks; just ask them.
If I am off for more than 4 days I can tell the difference; I’m still safe but I can feel the difference. Usually it manifests itself as a slight tunnel vision, not being able multitask as effectively and the impression of being behind the jet. Generally it clears up after a leg or two.