I have a 6 year old Siberian Husky.  When walking a couple a weeks ago, she had her normal bowel movement, then a little further on, she just sat down.  At first I thought something was still hanging there, but she got up and continued walking.  A little further along she sat again.  After that, I've noticed that when we walk, her tail is in the trailing position and in the house hanging down (usually it is curled up).  When we play or she gets excited, the tail curls up.  She did have another "sit" moment again last week.  She is not "scooting", there is no odor, I see nothing under there.  I can touch the rear area, pet and brush and she does not have any pain.  She eats, drinks, bowel is normal.
I haven't been able to find any information on this.
If it continues, I will take her to the vet; but she is not fond of that and you know how sibes are with their tails areas being examined.
This is my fourth husky and I've not encountered this before.  
Any thoughts?

Is she maybe over weight a little and just getting tired? I've also heard that thyroid issues can wear a dog out and cause muscle fatigue.

Thanks for the input. She's not overweight and not tired. We walk 1 1/2 miles everyday.
We do have a vet appt this week.

Have you ever heard of "Wet tail?" My lab mix gets it sometimes if he over exercises... Its very common especially after swimming. The tail comes out and then instead of curling up just kind of drops down... google it and see if its maybe what you're seeing? It usually goes away on its own- we give him aspirin... but he is almost ten!

Does she have any joint or back issues? I've heard of similar incidents happening to dogs with bad knees, hips, and/or backs. If you trust her not to bite you, you may want to try gently feeling around and seeing if she has any areas that appear particularly sensitive to the touch. Try it both when she's feeling normal and when she is having an episode, it may give you an idea of if there's something wrong that would need a vet to investigate further. Either way, I'd still bring her in as it sounds like she may be in pain.