Good question, because this gets to the heart of Buddha Dhamma.
The Buddha addressed the issue of future-suffering in the rebirth process.
– Each living being is born only to go through aging, sickness, and eventual death. But it does not end there.
– That living being is born again, only to got through the same process of aging, sickness, and death.
– Furthermore, most births in that rebirth process are in the four lowest realms (apayas) of animal, hungry ghost, asura, and hell. We tend to think of “birth’ as “birth as a human.” But in the rebirth process, human birth is very hard to get.
That is called “suffering associated with the rebirth process” or “samsaric dukkha.”
– The only way to end that suffering is to stop the rebirth process, i.e., to attain Nibbana.
The Buddha realized the “hidden suffering” in the rebirth process when he saw the “Four Great Omens” as a young Prince. See, “Buddhahood Controversies – Introduction“