jack russell won't jump on couch

My female 8 year old jack russell won't jump up on the couch. She stops at the edg of the couch and makes the movement like she's going to jump but she doesn't. And get ears are pinned back cause she looks scared that she can't jump up on the couch. Also when you pick her up to put her on the couch she's shaking a little. Does this have anything to do with deer ticks? Seems weird all of a sudden. She probably hasn't been jumping up on the couch for a week.