sounds like trauma injury to me if there is no concussive symptoms and if you still have a full range of movement (without unbelievable pain doing so) you should be fine. see your entire skull is surrounded by what we call a "shroud" of muscle meaning from your ass crack to your chin is one tight muscle holding your neck up. you seem to have strained it refrain from banging your head and apply heat and cold because it is muscle. 10 minutes cold -> 10 minutes warm/hot in the shower. hyperextending it should be fine as well just go enjoy a nice nap with pillows aligning your neck with your spine. i play rugby union as a hooker/no. 8 and sometimes prop. this happens to me like at least once a week. 3 weeks after you heal i'd suggest you begin stretching your neck by putting your hand against your head and pushing your head into it (not too hard) for more info on that stretch you can go online.
hit head on headboard neck/shoulder pain lessening but still worried. continue using cold compress or go to doc? . no nausea no dizziness no memory issues eyes normal. still hurting at base of skull nearest to neckline left side of neck around collarbone area and at start of shoulder.