She's a Border Terrier, not your usual terrier with people, sometimes she's quite nervous of pretty much anyone, usually she's very soppy and loving, but she can still be nervous with you. She's very nervous of new people too, very very cautious about approaching new people. And very submissive, often, if you call her to you, she'll come, but stop 6ft away and roll over onto her back, she looks terrified while doing this and throws out stress signals left, right and centre, so I'm sure it's not because she wants a belly rub.
She'll often lie/sit down and shiver almost uncontrollably, you can see her visibly shaking. She's still fully responsive, she'll respond to her name and walk around etc but as soon as she sits/lies down she'll start the shivering again. I'm not sure if she's shaking with nerves or excitement
Photo included just cos she's so frigging cute! This was the day she was stripped.
I meant to add, she's a rescue, approx 4-5yrs old and we've had her exactly a year tomorrow. I know nothing about her background. She used to hate DH, would growl at him when he came home from work, she loves him now though, is happy to snuggle up to him on the sofa in the evenings.
I have an 8 year old Border Terrier and he often does it. I'm not sure if it's a BT thing! Mine shakes when he's excited, not sure what's about to happen, scared, you name it and likes yours sometimes will just be lying quietly shaking. Nothing to worry about :-)