I am so sorry for your wonky neck. I hate waking up with one of those.
The neck isn’t usually stiff by itself in isolation. it’s usually stiff along with a whole system of muscles that hang onto the scalp. (medical english/normal english) These include the frontalis, temporalis, and occipitalis muscles, affecting eachother by their mutual attachments to the galea. / These include the muscles of your forehead that you can feel just above your eyebrows, the muscles on the sides of your head above and slightly behind your ears, and the muscles at the back of your head where your neck goes into your scalp.
All these muscles hang onto your scalp, which can slide around like a helmet that’s loose on your head (galea = helmet, Latin). If you move your scalp around with gentle massaging fingers you can often feel which of these muscles is achiest. Working on your forehead and the muscles above your ears with your own fingers, with heat, and with vibration often loosens up the whole system enough to start the neck muscles relaxing.
If you have been stressed a lot and “bearing the weight of the world on your shoulders” then another part of the system that is frequently tensed up is your trapezius. The origin of the trapezius, which is the spot on the model where the arrows are pointing, needs massage for the whole thing to let go when it’s overtensed.
If you haven’t got a friend willing to dig around in your back with strong fingers to find it, you can massage the darn thing yourself by finding a door frame with an edge that’s not too sharp, backing up to place the vertical hollow between your shoulderblade and spine against the doorframe, and doing whatever you need to do (standing on tippytoes, raising your body, bending your knees) to rub the tight spot, as if you were a horse scratching itself against a fence post.
I sometimes have fun with new coworkers by telling them I know a secret spot where they are carrying tension that will hurt and then cause relief. I rub the trapezius origin. They all to a woman (okay, the occasional man) fall forward across their desks exclaiming about the extraordinary secret spot and how did I know that about them.
If I were a con man (woman) I could make a bundle with that…
Good luck on your headache. Oh, I also find a constant background level of anti-inflammatory helps the damn thing go away more effectively with massage than heat or massage alone. Assuming you’ve got a normal body without bad kidneys, a loading dose after breakfast (never take nonsteroidal anti-inflammatory drugs on an empty stomach) followed by a low dose every few hours throughout the day does it for me.