There is a BIG difference between a horse whose nervous system is disturbed by the mineral/nutrient imbalances in Spring (or Autumn) grass and one that merely has excess energy from 'sugars'.

Cape-weed, especially when it has been mowed, can cause ‘neurological’ issues in horses. Sometimes signs are only mild as in being spooky but occasionally they are far more serious

Horses that are ‘down’ on their nutrition tend to be affected more often and more seriously. Especially when it rains after a dry spell and the grass greens up! Well mineralized horses are more resilient and tend to be less affected.