Have a friend who woke has a hard marble size lump under skin at base of skull.Popped up overnite. Is sore to touch and hurts when she turns head. No other symptoms. General good health. 51 yrs old. Was born with some fuses verterbrae in neck but no residual problems
Hi, sudden lump behind neck with pain is suggestive of an infection like an access. If he has no signs of toxicity like fever, he can wait till it resolves. He can use hot fomentation for pain relief and also Chat Doctor.  If it won't make a pus point in 4-5 days, consult a physician. Hope this helped.