Many things can affect how your body responds to a symptom and what kind of care you may need. These include:

• Your age. Babies and older adults tend to get sicker quicker.
• Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
• Medicines you take. Certain medicines, such as blood thinners (anticoagulants), medicines that suppress the immune system like steroids or chemotherapy, or natural health products can cause symptoms or make them worse.
• Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
• Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.

Neurological symptoms—which may be signs of a problem with the nervous system—can affect many body functions. Symptoms may include:

• Numbness, weakness, or lack of movement in your face, arm, or leg, especially on only one side of your body.
• Trouble seeing in one or both eyes.
• Trouble speaking.
• Confusion or trouble understanding simple statements.
• Problems with balance or coordination (for example, falling down or dropping things).
• Seizures.

Pain in adults and older children

• Severe pain (8 to 10): The pain is so bad that you can't stand it for more than a few hours, can't sleep, and can't do anything else except focus on the pain.
• Moderate pain (5 to 7): The pain is bad enough to disrupt your normal activities and your sleep, but you can tolerate it for hours or days. Moderate can also mean pain that comes and goes even if it's severe when it's there.
• Mild pain (1 to 4): You notice the pain, but it is not bad enough to disrupt your sleep or activities.

You can get dehydrated when you lose a lot of fluids because of problems like vomiting or fever.

Symptoms of dehydration can range from mild to severe. For example:

• You may feel tired and edgy (mild dehydration), or you may feel weak, not alert, and not able to think clearly (severe dehydration).
• You may pass less urine than usual (mild dehydration), or you may not be passing urine at all (severe dehydration).

Many prescription and non-prescription medicines and supplements can cause headaches. A few examples are:

• Medicines that contain hormones, such as birth control pills and hormone therapy for menopause.
• Medicines for erection problems.
• Caffeine (because of caffeine withdrawal).
• Some heart and blood pressure medicines.
• Vitamins.

Severe dehydration means:

• Your mouth and eyes may be extremely dry.
• You may pass little or no urine for 12 or more hours.
• You may not feel alert or be able to think clearly.
• You may be too weak or dizzy to stand.
• You may pass out.

Moderate dehydration means:

• You may be a lot more thirsty than usual.
• Your mouth and eyes may be drier than usual.
• You may pass little or no urine for 8 or more hours.
• You may feel dizzy when you stand or sit up.

Mild dehydration means:

• You may be more thirsty than usual.
• You may pass less urine than usual.

Symptoms of serious illness may include:

• A severe headache.
• A stiff neck.
• Mental changes, such as feeling confused or much less alert.
• Extreme fatigue (to the point where it's hard for you to function).
• Shaking chills.

Here are some examples of possible changes in your usual pattern of headaches:

• Headaches are worse than usual.
• You get headaches more often.
• The pain is in a different area.
• The pain feels different.
• The medicines you usually take for headaches no longer seem to work.