Hi, thanks for asking from HCM.
I can understand your concern. The popping sound just after heavy weight lifting must be sudden neck muscle pull or tear at insertion point over occipitalis area.
The headache could be due to
muscular pain which increases after moving neck, pressing muscle while lying down, exertion.
Still to rule out any other possibility,
consult doctor for local examination of head and neck. He will check his BP, vision to rule out these.
At home, he can
: apply icepacks at local pain site
: apply painkiller gel like Diclofenac
: Take tab Diclofenac after prescription
: Avoid exertion, extreme neck movement, pressure at pain site.
Hope it will help him. Thanks. Take care