Lal said above: “.. In between the birth and death, a sankhata exists (tithi). However, it undergoes unexpected change (aññathā), and that gives rise to Dukkhadukkhatā. That is expressed by, “titthassa sankata lakkhanan, dukkha dukkhata“.”
That is against the statement in e.g. Introduction -2 – The Three Categories of Suffering, #1:
“Vipariṇāma-dukkha arises when rupa (both internal and external) change against our liking….”
Thus, change against our liking or unexpected change is aññathā, which causes dukkhadukkhata. This was also explained by Waharaka Thero in a YT video, the change to another (unwanted) state causes dukkhadukkha.
This is also valid in case one gets sick or injured, both are unwanted changes and cause dukkhadukkha.