You forget appointments. It's impossible for you to get organized. You start a project—then another and another—without any one of them getting done. You can't remember what you've just read, because your mind is wandering.

We all have our "moments." We might write them off to multitasking, age, anxiety or mood disorders. But if these moments occur more than just once in a while, and there's a pattern to them, you may have attention deficit hyperactivity disorder, or ADHD—especially if these behaviors affect your self-esteem, productivity, relationships and the quality of your everyday life.

If you thought ADHD was a condition relegated only to the young, it's not. If you had it as a child, it can persist and follow you into adulthood, especially if your symptoms were severe as a child or if you also suffer from depression or other forms of mental illness, experts say.

The number of adults in the United States thought to have ADHD is estimated at 5 percent, but that number is likely higher because few adults get diagnosed or treated for it. Adding to the difficulty in diagnosis is that the symptoms can be subtler, more varied and less clear-cut than they are in children with the condition.

Scientists are not sure what causes ADHD—and there are likely a variety of causes. Some experts theorize a strong genetic component, while others are examining the role of neurotransmitters; smoking during pregnancy; complications from pregnancy, delivery or infancy; brain injuries; nutrition; and physical or social environment.

There's no single test for ADHD. Instead, symptoms usually determine the diagnosis. If you're wondering if you might have ADHD, take a look at the most common symptoms below.

• Forgetting to keep appointments
• Forgetting to pay bills
• Forgetting to return calls
• Avoiding completing forms or reviewing paperwork
• Feelings of restlessness
• Trouble sitting still
• Frequently interrupting conversations or completing people's sentences
• Trouble coping with stress
• Trouble retaining information and/or following directions
• Impulsivity
• Problems prioritizing tasks and following through
• Low tolerance for frustration

Many adults with ADHD learn to live with the condition through their own coping strategies like exercise, adequate sleep, setting up systems, making lists and breaking up tasks into smaller components.

But if the condition is interfering with your functioning, you might consider consulting with your health care professional about a possible diagnosis and treatment. The Mayo Clinic says that though it's not curable, ADHD is treatable through things like medication, education, learning new skills and psychological counseling.