The way to tell if your horse is acutely foundering is not only will they walk with their front feet stretched forward and the hind feet tucked under to support more of the weight, but they will have a pulse at the back of the fetlock near where the bulb of the heal ties in.
You should NOT feel a pulse at the back of the fetlock. If you do call the vet RIGHT THEN, don't walk - run.
The hoof will also become warm to the touch.
The feet should be placed in cool water and all food taken away.
The vet will administer anti-inflammatories and restrict the diet to plain old grass hay.
X-rays in a week or so to show the degree of rotation. Then trimming and shoeing in response to the Xrays.
Diet will almost always be an issue after an episode.
Causes include, high sugar diet, stress, poor body condition - at the time, or excess body fat - at the time and idiopathic (AKA no clue why). Their is a link to insulin production and the amount of risk said horse will have to foundering.