There are many possible etiologies. The most likely scenario is that something is causing pressure on something else which is either causing that something to have an oxygen deficiency or causing it not to transmit a nerve impulse. Stress can cause a spasm in a blood vessel, for example. That spasm can reduce blood flow to the tissue that blood vessel serves. Stress can also alter the osmolality of the tissues, which can cause pressure on a nerve bundle. Inflammation can cause the same effect.
As a suggestion, you might ask your physician to prescribe valium for a week or two. Valium has a bad rap, but it really doesn't deserve it. Of course it is a physician prescribed drug. It has fewer side effects that most all of the alternatives. See if the problems go away. Use a very low dose of valium and take it with grapefruit juice to increase the half life. Don't drive.
Log the periods of weakness.
You need to get a glucose tolerance test. Abnormal blood sugar levels cause the body to reduce the glucose level by an alternative means, which uses fluid. This reduces the ratio of fluid to solid matter within the bloodstream and increases the propensity of the blood to clot or fail to properly circulate. Often, after a cery stressful experience (a death in the family) people turn to "pigging out" to deal with the situation. The excessive eating causes high glucose levels.
You need to keep on top of this.
You need an "axial traction test". Axial traction is applied during the period of weakness, and you immediatly learn if the weakness is resolved by the application of traction. Axial traction can be applied by having the patient lie on the floor and be pulled slowly along a rug pulling upwards along the spine. If the weakness disappears, the liklihood is that you have pressure on the nerves that pass through the vertebrae. Often this pressure is caused by stress, or altered osmolality.
It was advisable to return for the reading of the MRI.
Your present condition could be due to anxiety/panic attacks. They can manifest themselves in many ways, and the results can be long-lasting. It would be good if you can seek professional help from a psychologist, psychtherapist, counseling social worker, or someone who deals with panic disorders. Often, we have panic/anxiety attacks because there are things from our past that must be addressed, and the anxiety is reminding us that there are unresolved issues.
1. Get the results from the MRI.
2 Seek professional help for the anxiety/panic attacks.
Good luck.