I have a 6 year old maltese myself. I would start using glucosamine/condroitin and also look into physical therapy for the dog. Both could be an immense help. Good luck!
I am NOT a vet or doctor. I just remember almost everything I’ve ever read (not bragging, it’s a curse as well as a blessing).
This sounds like the possible onset of cannine arthritis. Next bout might involve both legs.
I think MomwithHope’s advice is good: “I would start using glucosamine/condroitin and also look into physical therapy for the dog. Both could be an immense help.” Also ask a vet about the possibility that your dog is getting arthritis and what to do if that’s the case.