Injury. Lifting improperly. Overuse, lifting too much, injury, or stress.
Self Protection. When the spine has injury, the muscles near the spine are automatically triggered to tighten up and spasm. This is one way your body protects itself from further damage. When this process goes on too long the spasm interferes with circulation causing the spasm to become hard and fibrotic. Helpful: osteopathic manipulation, massage, muscle relaxants, back strengthening exercises, yoga.
Muscle injury. Severe pain in the lower back is frequently related to muscle spasm. The complex array of lower back muscles may be injured by physical activity. Poor lifting mechanics may cause this injury, resulting in muscle spasm. Also, muscle injury may result from rapid acceleration/deceleration. This type of injury is frequently caused by motor vehicle accidents.
Depends. There are many potential causes of low back pain with muscle spasms. The most common causes are related to strain or injury to the mucles and/or structures of the lower spine. While a "cure" often depends on the actual cause, prevention can be obtained by maintaining a healthy weight, good flexibility, and a strong core. See your physician if you have pain greater than 2 weeks.
No. Back spasms often come from overused or injured muscles. Eating schrimp should not cause them.
Spasms. I wonder if you may have esophageal spasms that are felt in your back. The esophageal (foodpipe) spasms may refer to the back and that may be the reason why you feel them there. The pancreas pain may also refer to the back but it is usually severe and normally happens after meals, whereas esophageal spasms are usually during the meal.
Varies. There are multiple potential causes. It can me musculoskeletal, such as in a paraspinal strain; it can be from a pinched nerve in the back; it can be from things in that area such as a kidney or pancreas problem. I would not hesitate to be seen and evaluated for an accurate diagnosis.
A little vague. I'm not exactly sure what this could be but generally speaking those symptoms point to a low blood sugar (best case) or a cardiovascular problem (worst case). I would recommend being evaluated at an Urgent Care or ER today.