If every little thing keeps startling your dog, it can be due to several different reasons.  Any loud noise near your dog, like the noise of the vacuum cleaner, doorbell, or tv, can leave it startled.  Older dogs develop hearing and vision impairment, and they won't notice or near something or something until they are too close, which can result in them getting startled.  It is also possible that your dog is in pain and wants to be alone till it feels fine. If your dog sees someone getting close, he can get startled.  If there has been any significant change in your dog's routine, it can develop anxiety and stress, and everything would make it startled.