Misfire cylinder 2, 3 and 4

[germangs]

I had an abnormal condition on my 03 X5 6 cyl with 112k miles on it when all of the sudden I got a service engine warning light and engine abnormal shake. It was going on for a day or so then engine shake disappeared. The service engine light stayed on and I went to my friend to scan the codes where we detected codes 239, 240 and 241-misfire cylinder 2, 3 and 4. The codes got reset and things are back to normal. My friend said it could be the ignition coils or catalytic converter.
Why it happened and disappeared after all? What could be the issue that triggered that event?