Thanks for posting on HCM,
If you are experience sudden ankle pain with no swelling and the feeling that it is inside then it is most probably a non-septic arthritis
or arthrosis. You will require antiinflammatory drugs after being examined again by an orthopedic surgeon and after which he may decide to do an MRI
or CT scan
. Spontaneous tendon tear is rare but possible given that you use your ankle joint on a daily basis.
A previous or an old injury
could also be responsible especially if you do not remember any recent injury. Do not be surprise that you can have an injury even without an obvious trauma to your ankle. Just the mare fact that you walk daily can lead to a joint injury.
In any case, an orthopedic surgeon can better evaluate and provide you with appropriate treatment.
Hope this helps