The flu tends to come on suddenly -- you're fine in the morning and aching and shivering that night -- while a cold usually develops gradually over the course of two or three days. Flu usually causes a fever and aches; a cold usually doesn't. Other symptoms of the flu include headache, fatigue, cough, sore throat, nasal congestion, body aches, chills and, usually in children, vomiting or diarrhea.

How do I know if it's the novel H1N1 strain?

Unless your doctor orders a test, you won't. That test, which involves a swab of nasal secretions, isn't routinely conducted. Most likely, if your doctor thinks you have the flu, you will be sent home with advice on care.

In some cases, however, doctors will want a more precise diagnosis, which helps inform public health officials about outbreaks. A flu test is also sometimes given to people at risk of becoming very sick, such as hospitalized patients, infants and those with underlying health conditions. Healthcare workers may also receive a flu test.

In general, it's not necessary for you to know whether your flu is H1N1 or a seasonal strain. They are treated similarly and have similar effects, though this H1N1 strain seems to be transmitted especially easily among children and young adults.

How should I take care of myself?

Stay home and rest. You don't want to tax your body when it needs its strength to fight a virus.

Drink plenty of liquids to avoid dehydration.

Don't drink alcohol because it can increase the risk of dehydration and it weakens the immune system's response.

Don't smoke; that can worsen respiratory symptoms.

Do take over-the-counter pain relievers (but don't give aspirin to children or teens) for head and muscle aches.

To avoid infecting others, stay in a separate room in the household and try to use a separate bathroom. Wear a mask, if tolerable, when around other people, even loved ones.

When should I go to the doctor?

In most cases, a trip to the doctor isn't necessary because healthy people will recover on their own in about five days. However, if you have just become ill, you may want to call the doctor to obtain a prescription for an antiviral medication. Taking an antiviral, such as Tamiflu or Relenza, can shorten the course of the illness by a day or two if the medication is given within 48 hours of the onset of symptoms.

Doctors vary in their willingness to prescribe antiviral medications. In a recent update from the Centers for Disease Control and Prevention, doctors were advised to prescribe antiviral drugs only in certain cases -- to treat or prevent illness in people who are severely ill or hospitalized or at higher risk of having serious complications from flu, such as babies and those with underlying illnesses. Antivirals are not recommended for prevention or treatment of otherwise healthy people. These guidelines were issued to alleviate concerns over a potential shortage of anti-viral medications.

Consider seeing your doctor if you are at high risk for complications, such as developing pneumonia, sepsis or having a severe asthma attack. This includes people ages 65 and older, those with chronic medical conditions, pregnant women and young children.

Should an ill person go to the hospital?

Normally, no. But the virus can lead to other illnesses, such as bronchitis, pneumonia, sepsis and asthma flare-ups.

Here are some emergency signs in children:

  • Fast or labored breathing, indicating pneumonia or sepsis.

  • Bluish skin color, indicating the child may not be getting enough oxygen.

  • Not drinking enough fluids, which puts the child at risk for dehydration.

  • Not waking up or interacting, which can indicate a more severe case.

  • Being so irritable that the child doesn't want to be held, which can also indicate more severe illness.

  • A return of flu symptoms after the child appeared to be getting better, which could indicate that the child has developed a secondary illness or was misdiagnosed with the flu.

  • Fever with a rash, which can indicate an illness other than the flu.

And in adults:

  • Difficult breathing or shortness of breath, which could indicate pneumonia or sepsis.

  • Pain or pressure in the chest or abdomen, which could indicate a more serious case or that flu is not the right diagnosis.

  • Sudden dizziness, which can mean the person is not getting enough oxygen.

  • Confusion, which can mean the person is not getting enough oxygen.

  • Severe or persistent vomiting, which can lead to dehydration.

  • How long should I stay home?
    That depends. Your primary goal should be to avoid infecting others. Always stay home if you have a fever or think you may be coming down with the flu. Adults can spread the flu to others for up to five days after getting sick, so stay home until you feel better and for 24 hours after the fever is gone (without use of fever-lowering medications). You may have lingering symptoms, such as nasal congestion, cough or fatigue. That is normal. But if your cough or congestion or any symptom hasn't abated much from its peak, you could still be infectious. Sources: U.S. Centers for Disease Control and Prevention; Dr. Aaron Getty, spokesperson for the Infectious Diseases Society of America; L.A. County Department of Health Services.