Question: Any explanations for this good day???

Now that I have realised that the tips and swing thoughts that I have been exaggerating (and destroying my swing) are things that I was probably always doing right (luckily), I have gone back to a swing that feels comfortable, compact and repeatable.
One thing is puzzling me however. Both last year and this year, during good consistent spells, I had one day (yes just ONE!) where I was driving the ball easily forty/fifty yards further than normal. In fact it was rediculous but you could easily get used to it!!!
I think on both those occasions, I was standing tall and feeling strong and didn't notice if I was swinging particularly fast, just had this strong, powerful, confident feeling.
Could the feeling of standing tall be the thing???
I remember I had the feeling of stretching my arms out, not quite reaching for the ball and not in an uncomfortable strangling the club manner.
I think that normally on the backswing, I don't keep my left arm too straight but manage to hit the ball reasonably long and straight.
So, if someone has a reasonable swing (but has slightly bowed arms at address and slight elbow break at the top of the backswing but manages to hit the ball well enough) suddenly straightens out the arms at address and keeps the left arm reasonable straight on the backswing, would this explain the serious extra distance and confidence??
I know I should be out there trying this out (and I will), but I just wanted to hear your thoughts on this.

It could be that your shoulders were more relaxed on that day. I've seen a lot of players hunch up their shoulder so they look like a turtle at address. If you do that you'll have no end of trouble.

If anything I feel my shoulders are pressed downloads a little though they have no stressed tension in them. I also like to feel my arms hang more naturally (verticle) or even pulled in a little. Ben Hogan in his book - 5 lessons (a golf bible) says that the elbows at address should point to their relevent hip bone and the elbow socket should be pointing outwards away from you slightly.

Whatever you do if golf don't try and change too much too soon otherwise your swing will degrade (some aspects of it may be ok anyway) and you'll have a miserable time hitting the ball sideways.

Paul