suru verb (special), intransitive verb
lie down (in bed); take to one's bed
Rare, literary verb for lying down, especially due to illness. Modern Japanese normally uses 寝る or 横になる.
病を得て、彼は長く床に臥した。
He fell ill and lay in bed for a long time.
The kanji 臥 means 'lie down' or 'bend down'. The reading がする is a native Japanese verb; the exact derivation is uncertain, but it is a rare literary form.