I mean, your hearing aid and ear mold are together. So, if you take the ear mold off... the hook part would come off too, wouldn't it.
Since the ear mold stays in place, then it's understandable for the hook part to fall out from behind your ear and hang loose... but not vice versa unless your ear mold was small or needed to be replaced.
Unless... you're talking about the biege hearing aid - clear plastic hook - tube - ear mold? So, when you try to take the tube off... the hook unsnaps from the hearing aid? If that is the case, it depends on the hearing aid. Some hearing aids have easy snap-on and snap-off for those hooks. Some hearing aids have a twist on hook (like my old analog hearing aid). That's something you're better off asking your audiologist (where you got the hearing aid from) since they would know the hearing aid better than us.