Just like people, horses experience nervousness. Some horses are more susceptible than others, based on their breeding or rearing, for example. Not all tension is bad.
Horses and humans both need a certain amount of tension to perform to the best of their abilities, but constant pressure or stress increases the likelihood of health problems. Ensure that your horse gets adequate exercise and has a pleasant stable environment and a healthy diet.
A horse’s diet can have an enormous influence on nervousness and behaviour.