behaviour change?

Question
Hi, i have a 6 year old Newfoundland dog. He is usally very quiet, calm, relaxed.. etc.. But recently in the last day or so, he's become alot more jumpy/scared. As an example.. I walked up to his rear end, placed my hand on him, immediately he let out a loud yelp and ran away, shaking. Normally he would have just stood there and not bothered. This has happened 3 times in 1 hour, what could have caused such a reaction so suddenly? He doesn't do it if you come up to him head on or talk to him from behind and get him to look at me first.

Thanks

Answer
I would honestly have him checked out by a vet. With this coming on so suddenly, I worry that he possibly has an injury or something else medical going on that you can't see. Has he been diagnosed with hip dysplasia? His hips could be bothering him and when you come up behind him, it startles him because of the pain. Or he may have a problem with his hearing with being he's fine if he looks at you first. I would get him checked out and see if anything is diagnosed.