medication mix-up

I've done something very stupid, but thought I would post it to warn others.
I take Atenolol daily since a heart attack in 2006.
After my recent operation I was given some codeine for the pain.
But they are in almost identical packs, and the tablets themselves are almost identical, small round white.
This morning I realised I've been taking codeine (which I don't really need) instead of Atenalol. for nearly a week!
I managed to get a Dr. appt and he said not to worry etc. But I've been feeling very strange and 'woozy', during the night too, so hope I've learnt my lesson.