The memory loss from stress is not the same as memory loss from a physical head injury.
Stress related memory has to do more with perception. Prolonged stress tends to 'flatten' the perceptive process, you notice only things related to the stressful situation that occupies your mind. The conscious mind tells the subconscious mind "These are the important things," and the subconscious mind does it's best to provide only relevant information and withhold the rest.
It's not that memory loss causes things to be forgotten, but that they are deemed to be not important. When the same stressful state of mind is repeated day after day, the mind becomes conditioned to react to the pressures in specific ways, and that includes selective remembering.
The danger from stress is not simply memory loss, but the fact that the way you think about yourself, your loved ones and the world changes negatively.