Maybe it starts with simply forgetting something.

You can't remember the route to a restaurant you've been to many times before or the birthday present a friend gave you a month ago.

Then comes the worry.

Is your forgetfulness a sign of something serious? Such brain freezes happen to most of us, to different degrees, as we age. Even experienced public speakers have their "oops" moments, when a word or term they use on a daily basis simply refuses to come to mind.

But while such common memory lapses are frustrating, they don't necessarily mean you're losing your marbles. If your lapses aren't disrupting your life, there's no need to be actively worried, experts say. 

"The key issue is whether cognitive changes are significantly interfering with daily activities," says Kirk R. Daffner, M.D., chief of the division of cognitive and behavioral neurology at Boston's Brigham and Women's Hospital. If that's happening, you should consult your doctor. Your lapses may well have very treatable causes. Severe stress, depression, a vitamin B-12 deficiency, insufficent sleep, some prescription drugs and infections can all play a role. 

Even if those factors don't apply to you, your memory isn't completely at the mercy of time. Studies have shown that people who exercise, stay mentally active, socialize regularly and eat a healthy diet can minimize memory loss. 

Still worried? Here are six types of normal memory lapses that are not a cause for worry.

  1. Absentmindedness
    Where in the world did you leave your keys? Or why the heck did you walk into the living room anyway? Both of these very common lapses usually stem from lack of attention or focus. It's perfectly normal to forget directions to somewhere you haven't visited in a while. But "if you've lived on a block for 10 years, and you walk out the door and get lost, that's much more serious," says Debra Babcock, M.D., of the National Institute of Neurological Disorders and Stroke.

  2. Blocking
    This is the frustrating tip-of-the-toungue moment. You know the word you're trying to say, but you can't quite retrieve it from memory. It usually happens when several similar memories interfere with each other. A 2011 study, published in the journal Brain Research, showed that elderly participants had to activate more areas of the brain to perform a memory task than the study's young subjects. "We're all accessing the same brain networks to remember things," says Babcock, "but we have to call in the troops to do the work when we get older, while we only have to call in a few soldiers when we're younger."

  3. Scrambling
    This is when you accurately remember most of an event or other chunk of information, but confuse certain key details. One example: A good friend tells you over dinner at a restaurant that she is taking out a second mortgage on her home. Later, you correctly recall the gist of her news but think she told you during a phone conversation.
    Research points to the importance of the hippocampus - a region of the brain crucial in the formation of memories about events, including the particular time and place they occurred. Scientists estimate that, after the age of about 25, the hippocampus loses 5 percent of its nerve cells with each passing decade.

  4. Fading away
    The brain is always sweeping out older memories to make room for new ones. The more time that passes between an experience and when you want to recall it, the more likely you are to have forgotten much of it. So while it is typically fairly easy to remember what you did over the past several hours, recalling the same events and activities a month, or a year, later is considerably more difficult. This basic "use-it-or-lose-it" feature of memory known as transience is normal at all ages, not just among older adults.

  5. Struggling for retrieval
    You were just introduced to someone, and seconds later, you can't remember her name. Or you saw a great film, but when you tell a friend about it the next day, you've completely forgotten the title. Aging changes the strengths of the connections between neurons in the brain. New information can bump out other items from short-term memory unless it is repeated again and again.

  6. Muddled multitasking
    At some point the number of things you can do effectively at one time diminishes. Maybe you can't watch the news and talk on the phone at the same time anymore. Not such a bad thing, really. Studies show that, the older we get, the more the brain has to exert effort to maintain focus. Further, it takes longer to get back to an original task after an interruption. - Mary A. Fischer