Sudden neck pain and fever?!

Flu and other viral infections can cause muscle stiffness.

Meningitis can cause stiffness in your neck, but this would be stiffness in your spine, not your neck muscles or upper back muscles. If trying to bend your neck to touch your chin to your chest causes severe pain and your fever spikes to over 102, call an ambulance because you have meningitis and you could be dead within hours without treatment. You are not showing either of these signs, so it is clearly not meningitis.

Meningitis causes swelling inside the spine and the brain, not soreness or stiffness in muscles. It is known for fast onset (hours), but an overnight onset is more likely flu or other viral illness.