Check for ear infection, tooth damage, something that might have triggered pain that is not obvious.

 Quote: vivek sagar

hi to all once again.it is important and urgent.why this happened to me.
the dog came to me.
i along with my son were sitting on the bed.he approached both of us
and we entertained him.
he put his head on the bed and we petted him.
after 20 seconds he immidiately showed aggression (Growled & Nipped).

I am not a professional K9 trainer or behaviorist, so you may disregard my view if you wish, Vivek...

But this dog does NOT look like a SAFE PET for a Family with Children -- He seems to consider himself SUPERIOR to your Young Son and other "underlings" in the human household, Demanding their Respect, while giving them BAD grief in return...

You freely admit to Not Understanding the dynamic here, and consequently, it appears that you do not have the Expertise Level needed to Prevent Escalation of this dog's unacceptable Pack Structure infractions -- The situation is NOT improving ... IMHO, you are putting the well-being of Your Family at risk for the sake of keeping this animal as a HOUSEPET

Thanks candidates and all of you for nice advice.

Sorry candi

hello team, this is happening since last four days. at the time of morning evening walks, suddenly my dog started to fear tail down and pulling hard.(day 1) i tried to pacify but no help. on the way three stray came and up to this time no problem and when they followed, my dog became a little bit disturbed, defensive and tried to interact by raising hair line.(day 2) when we reached home and unhook the dog he ran straightway in to the corner of room. repeated this feared state of walks.(day 3 and 4). tomorrow would be 5th day and i will observe what happens. prior to this incident, while taking dog to walk some children rushed to my dog to pat and i refused straight way then the children raised the noise by taking the name of dog and just after that dog became little nervous. your expert advice is requested. this is the same dog about which this thread is opened. and right now after evening walk i unhooked collar and at this time he growled and rushed in to the room. i protested this growling by saying no and made a time out for 2 minutes and after that i tied him.

THis dog is vaccinated for rabies, yes?

I only mention this because a big change in personality, fear followed a day later by signs of aggression, could be a symptom in an unvaccinated dog, in a country where the disease is common.

Yes dog is vaccinated

I am not a trainer. So I just have an idea, that's all, no expertise.

Perhaps if you would stand between your dog and strays, children on the street etc, make it clear that you are going to handle all these confrontations, and he doesn't have to do anything, doesn't have to growl, or raise his hair, or act tough -- if he could learn to count on you to do this for him, he might become braver, and less reactive.