<human>: Can you provide a brief overview of the text?

I just wanted to share my experience I have had with my dog.  I have had my lab since he was 8 weeks old and he is now about 1.5 years old.  I have spent lots of time training him and have even gotten him registered as a therapy dog.  About a couple of months ago he started to act a little different at home.  He started to become territorial and aggressive to new people who would come to my house.  He even tried to bite a lot of people.  It was sort of Jeckle/Hyde syndrome.  When he gets in these states its almost like he had ADD and wouldn't listen.  But once we calmed down a little bit he would snap out of it and be his normal happy self.    I took him to the vet and they said he was perfectly healthy. Since this was now outside my level of expertise I consulted some trainers who all said he is becoming an adult and this is just who he is now and if i was not willing to accept who he was i should put him down.   I refused to accept that.  In my mind there was no reason for this change in attitude.  So i brought him back to the vet and demanded they test his thyroid levels...

It was determined he had low thyroid levels and needs to be on thyroid medication.  Once i put him on this medication he  was his normal self and does not react to strangers coming to my house.  He is happy and not scared of strange things in the house.  I'm telling you my story because a lot of times people overlook that their dog might have a thyroid problem because they don't show the normal symptoms of lethargy, weight gain, or hair loss.  My story has a happy ending and I wanted people who are in a similar position to be aware of this.
<bot>: If your dog is reactive/aggresive all of the sudden PLEASE PLEASE get their thyroid levels checked before you deem them a lost cause.