Are dogs born with instinct? Of course! If you get a cattle dog, they will have the instinct to herd. If you get a beagle, they will have their noses to the ground. Can those instinctual behaviors manifest into bad habits? Yup. For example: your cattle dog nips at the heels of people who move to fast (that is instinct). You let it go and let it go and let it go...and then suddenly you want it fixed. Now you are working against instinct AND habit.
All too often I see dogs with behaviors that are troublesome. And worse: engrained. What that means is that they have been exhibiting the behavior for a long, long while. And if we don't give them new habits, those bad ones become the only ones they know. And if that behavior has been going on for a while, it will take some time to modify. And you may need a professional.
Before contacting a trainer, however, here is what you will need to do. Ask yourself if you have seen ANY signs of the behavior in the past--even small ones. If you really can't see any, contact your vet. Often sudden behavior changes have medical reasons. If you can find clues that the behavior was present, contact a trainer and be prepared to work.
Here is my point: as soon as you realize a behavior is manifesting in such a way that COULD be a problem down the road, call a trainer for help. If your puppy growls when you try to take a toy away, that may be cute to you but when the dog he becomes does it, it is suddenly an issue. Your 5 pound puppy jumps up to greet you? Adorable. But when that puppy turns into a 40 pound dog and jumps on your small child, it isn't so dorable. So, the thing is, it wasn't sudden. It had BEEN an issue. You just didn't realize it.
When you reach out to a trainer, be honest--don't hold back. We can't help you if you don't tell us everything about when the behavior started, what you have done (good and bad) and how often the behavior occurs. And please realize that if the behavior has been happening for a while, it will take time for the behavior to be modified. You and the trainer will be working to create new habits--and if you think of how hard it is for you to create new habits, THAT is what we are working with. It will be difficult to give a clear time line of when the behavior will be modified, but what I can say is that if you are dedicated and consitent, you will see results. But you will have to be patient. It could take time. Weeks. Months. But it can work. And it will.
How do I know? Because the minute I knew Gracie had anxiety, I reached out for help. And as soon as I realized that Garmin had intense leash reactivity resulting in redirected frustration? Worked on that, too. If I didn't, those problems would have simply gotten bigger. They would not have gone away. Are they gone completely? Nope--in fact, some of those behaviors will never completely go away. They can be modified. And managed. But they may never go away.
Never be afraid to ask for help--it's how we learn and how we grow as dog owners. But, the sooner you reach out for help, the higher the probability that you will be able to turn it around. Would it be easier to give up? Probably, but you owe it to your dog to try.