Your dog may be jumpy for the following reasons:
Environmental Causes
These are things outside of your dog that can lead to his being jumpy. For example, the doorbell, vacuum cleaner or another loud noise can lead to jumpiness in your dog. He may feel startled as a result of those sounds.
Hearing and Vision Impairment
If your dog is having trouble with his vision or hearing, he may not notice that a person or another animal is coming near him and he may become surprised. In particular, as your pet adjusts to the change in these important senses, he may experience a nervousness not typical to his personality. There are things that you can do to help your dog be more aware of your approaching him.
Stress and Anxiety
Changes to your pet’s routine, a change in the household dynamics or an illness can all initiate jumpiness in your pet. If your canine is used to having companionship and the household changes, he may be jumpy as he adjusts to the differences. Anxiety due to changes or due to illness can also bring on less relaxed behavior.
Pain
Your dog may be experiencing dental pain, pain from a growth or from an injury that could cause him to jump as the pain hits. A veterinary consult can shed some light on discomfort that may not be evident to you but that is causing your pet to be uncomfortable.