Probably a semantic development ‘to become healthy, mature’ < ‘to attain puberty’ < ‘to have nocturnal ejaculations’?
PWS
*ḥlm - to dream; have nocturnal ejaculations when dreaming
(SED I No. 25ᵥ; HALOT 320)
There is no trace of *ḥlm ‘to dream’ in Akkadian, where the nominal
concept “dream” is expressed by šuttu, a secondary
formation from PS *šin-at- ‘sleep (Kogan 2015: 83)