To solve this problem the brain often has to rely on memory cues or bits of information related to the thing we're trying to recall "to jog" our memory. Pretty much anything can serve as a cue, as long as it's associated somehow with the information we're looking for.
As it turns out, the brain uses our mood state as it's single most important memory cue. Believe it or not the brain tags every one of our memories according to the emotional state we're in when the event occurs. And whenever we're in the same mood this serves as a powerful retrieval cue.
When you're sad, for example that despondent mood triggers all sorts of memories from other moments when you were sad or in low spirits. When you experienced a sense of failure, during times of loneliness and rejection all show up and it becomes difficult to remember any specific times in the past when things were going well. If you are in a relationship that break up all you can think about are all the other break-ups in the past you can't remember the good times that you had with anyone. It becomes a downward spiral of reminiscing.
When you are overwhelmed with stress, you might identify with a decline in your emotional health. Besides being quick tempered and easily agitated your memory may also be affected. Stress is frequently the result of a chaotic schedule, and with too much to do, when stressed it's not unusual to forget things.
If you are feeling stressed out and "scatterbrained" you need to spend time improving your concentration to relieve overload and overwhelm during times of extreme chaos and tension. When your attentiveness decreases, it's up to you to regain control.
There are a few ways to increase your mind's ability to perform during duress. My first choice is to exercise. Exercise helps your brain generate new cells that are linked with the enhancement of memory. Physical exercise increases oxygen to the brain and increases neural firing.
If you feel isolated because you work long hours, or home taking care of your family or you don't drive or for whatever reason - find new friendships. Make sure you socialize with the friends and family you have. Invite a friend to dinner or out to lunch. If it's someone you work with don't talk about work. And if you can't get out to meet your friends or meet new people develop new friendship with people you meet on-line. There is a whole world out there and a lot of people are lonely and would love to find a new friend. This give the brain a new workout as you adjust to a different conversations in a new environment all while activating or re-activating different senses.
If you have a long drive, consider listening to an audio book. You'll be surprise how delightful you drive becomes and the traffic becomes much less stressful allowing you to arrive at your destination in a much more relaxed state. You can also break-up the routine of the drive by trying a new route once in a while. If you normally drive on the highway find a route that allows you to drive on a country road.
Stress doesn't have to cause your memory to decline that is if you don't allow it to. As long as you give your mind a workout by creating new neural pathway the same way you would build new muscles when you work out your body, you'll have a healthy memory that allows you to remember the important things during times of stress and anxiety.