When my golden retriever is startled awake he has just begun having a strange reaction. At first he will come running and will even bark sometimes. But then he will suddenly start to shiver, have trouble standing, his tail will tuck under and he has trouble holding his head up. This lasts for about 3-4 minutes and then he is suddenly OK. He is 5 years old and this has happened twice in the last month. Is he having a seizure? Or could it be as simple as he isn't fully awake at first?

His tail between his legs definitely indicates insecurity, and that could easily turn into aggresion if it's not dealt with. Has something tramatic or anything out of the ordinary happened to him in the past month? Has his routine changed? Has he recently been frightened by a loud noise, or has maybe been acting anxious?

I would get him checked out at the vet to rule out anything neurological. This is not normal behaviour if he never used exhibit this before. Better safe than sorry. I would tell the vet exactly what happens when he is startled, and how long the shaking lasts, exactly when it started and have him do tests for any disorders he may have.

Good luck!