I m a female, 18 years old about 5 4 and 110 pounds (not sure if this is of any relevance, but just in case) i have a bit of a fat pocket or buffalo hump (so my family doctor says) behind my neck and it s generally flat and unnoticeable...pretty much non-existant unless i m tense. I also noticed that when i smoke marijuana (about once or twice every weekend, give or take) my upper back, shoulders and neck tend to tense up and it becomes very difficult to sit up straight and relax. I do think that my posture may need some work, it is much easier to correct bad posture after a good massage - this relief usually lasts a couple weeks, or until i get high/stressed out again. This tension effect lasts for a few days. What could be the cause of this?