my dog once in a while lays down with her right leg stiff and her front leg tucked in and can't move her right side. you call her and she does'nt respond it seems like she is staring into space, and she shakes.this last about 30 min and then shes back to normal. she is 5 yrs old.when shes normal is is very active. she does this 1 or 2 times a week.