What is the sickness of death (marad al-mawt) that Hiba (a gift) is recognized by, and when is Hiba considered a will?

The "death illness" (marad al-mawt) which renders its owner incapacitated is determined by the judgment of physicians. Every illness that is deemed to frequently lead to death is considered a death illness, even if it was previously considered dangerous but has now become easy to treat. A gift made during a death illness is treated as a bequest (wasiyyah); thus, it is not valid for an heir, nor can it exceed one-third of the estate, unless the other heirs permit it. Its validity is contingent upon it not exceeding one-third of the estate or upon the heirs' permission. The calculation of whether it exceeds one-third is made at the time of death.