The more often you fly, the more you can take on, and vice-versa. As an instructor, when I'm flying helicopters every day it's no big deal to fly, talk, watch the student, keep a good lookout etc etc etc. But recently, after a week off with a cold and then two weeks holiday, I could do it, but it was much harder work. And when I used to only instruct at weekends, it was utterly exhausting, and I missed little things - I just didn't have the spare capacity. I fly fixed wing aircraft every month or so, and it's fine....but only if I'm careful and don't take on too much.
So I too think you did rather well after five years. And the more you fly, the more you'll find you can do without errors creeping in. But doing well or badly has nothing to do with it, and is a bit meaningless really. Everybody's different when it comes to how often they need to fly, and how quickly they get rusty. The important thing is that you know how it works for you. You ask if the only thing to do is get back in the saddle. Yes, but also do exactly what you're doing - notice when you make mistakes and realise it's due to overload/lack of practice. That way you gradually learn how much you can take on if you haven't been flying for a while. You can also start to notice in the air if you're getting overloaded; that's much harder, as there's not enough spare capacity for any bit of your brain to stand back and recognise the symptoms. But little things, like realising you missed a radio call, or can't keep your altitude, or just suddenly don't know where you are...they're all clues to have a look at what's going on, and take the pressure off yourself a bit if you can. I tend to carry a GPS, not even switched on; it's a useful backup if you get a bit overloaded, as you can at least ease off on the navigation for a bit. There's no shame in recognising that you've reached your personal limit. But what you experienced is perfectly normal; I'd be surprised if you hadn't.
Very important topic; thanks for bringing it up.
