We used to have a little Lancashire terrier dog which on occasions used to tear round the house like a wild thing at great speed for no apparent reason. Backwards and forwards it rushed expending excess energy just for the sake of it. My Mother used to say, "it's having a light do" meaning it was behaving rather bizarrely. We all knew what she meant but I've often wondered what was the origin of this phrase. Has anyone heard this and can anyone please explain?
I've no idea where this saying originated, so I can't answer your main question soz :(
I can, however, join in and say that this "light do" that your dog was having, seems to happen with small dogs more than larger dogs (in my experience anyway).
We used to have a cross Lancashire Heeler and she'd do what you described - running around the room for no reason.
We've now got 2 Yorkies and they're exactly the same - one will usually start the other one off and they both usually end up playfully chasing each other round the room .... fun to watch lol :)
My suggestion: the word 'do' is often used to mean some kind of party, get-together, occasion for celebration, as in 'we're having a bit of a do for her birthday.' In northern England, the word 'right' is still used to mean 'very, emphatically so.' Could your mother's expression have been derived from 'having a right do'? Meaning; having a very good time; bit of excitement.
Yea I've heard of the expression, "having a right do" .... but not "light do".
Maybe your mother misheard the original saying and she ended up saying "light do" instead of "right do" ??