the world > health and disease > ill health > be in ill health [verb (intransitive)] > be weak > become weak > of parts (3)
Of the limbs: To give way, totter.
= flag, v.1 in various intransitive senses. To become languid or flabby. Of a garment: To fall in folds. Obsolete.
intransitive. Of a vessel or opening in the body: to collapse inwards, so as to cause obstruction. Obsolete. rare.