This is not a good answer but the same happend to mine 3 years ago.Then one afternoon when i came home from work i found it had just fallen over .I can only guess..but i think the roots were weak and the tree did lean to oneside,so the top weight pulled it down..my tree was about 7 foot. :-((

We have a laburnum that is very high and should really be.

taken back a bit by proper tree surgeon, as it has a lovely Paul's Scarlet

growing through it to about 2/3 of the way up. If the tree is not huge like ours with thick limbs. You might reach your ailing branches with an extended lopper, and be able to remove them, if it is not too thick. We had a previous laburnum there and it went ailing and mishapen. A tree surgeon working next door added that job to his work and we paid . As in the first comment it had a poor root system and came up easily.