How long does a muscle spasm last?

so during 5th period which is english class, i sat down and felt excruciating pain on my right neck area. i went to the hospital and my doctor said it was a muscle spasm. she then injected me with anti-inflammatory and gave me motren. its been a day and i sleep from 12AM to 2PM 12 hours in bed , when i woke up i still felt the same pain, what to do?? The reason im asking is because its been 24hours since i went to the hospital and my doctor said it would go out in a couple of hours. but i still feel the same pain if i try to move my head to the right area.