According to the New York Times Health Section:
http://health.nytimes.com/health/guides/disease/sickle-cell-anemia/complications.html

[On a personal note, the New York Times article on Sickle Cell Anemia is completely accurate.  The New York times article really gives you an in-depth, easy breakdown of what Sickle Cell Anemia is, how it is inherited, the effects it has on those who have it and the complications of the disease.  All in all, the main Sickle Cell Anemia reference websites, could definitely use some updating and refreshing, to help all those who visit their site seeking help and or answers.]

Pain and Acute Sickle Cell Crisis
The hallmark of sickle cell disease is the sickle cell crisis (also sometimes known as a vaso-occlusive crisis), which is an episode of pain. It is the most common reason for hospitalization in sickle cell disease. The pattern may occur as follows:
• In general, the risk for a sickle cell crisis is increased by any activity that boosts the body's requirement for oxygen, such as illness, physical stress, or being at high altitudes. In more than half of episodes, however, the trigger is unknown.
• Episodes typically begin at night and last 3 - 14 days, accelerating to a peak over several days and then declining.
• The pain is typically described as sharp, intense, and throbbing. Severe sickle cell pain has been described as being equivalent to cancer pain and more severe than postsurgical pain. Shortness of breath is common.
• Pain most commonly occurs in the lower back, leg, hip, abdomen, or chest, usually in two or more locations. Episodes usually recur in the same areas. Pain in the bones (usually occurring symmetrically on both sides) is common because blood obstruction can directly damage bone and because bone marrow is where red blood cells are manufactured.
• The liver or spleen may become enlarged, causing pain in the upper right or upper left sides of the abdomen. Liver involvement may also cause nausea, low-grade fever, and increasing jaundice.
• Males of any age may experience prolonged, often painful erections, a condition called priapism.
Episodes cannot be predicted, and they vary widely among different individuals. Episodes sometimes become less frequent with increasing age. Generally, people can resume a relatively normal life between crises. Most patients are pain-free between episodes although pain can be chronic in some cases.
Acute Chest Syndrome (ACS)
Anemia
Anemia is a significant characteristic in sickle cell disease (which is why the disease is commonly referred to as sickle cell anemia).
Severe worsening of anemia. Children, adolescents, and possibly young adults may experience what is called splenic sequestration. This happens when a large amount of the sickled red blood cells collect in the patient's spleen. Symptoms may include pain in the right abdomen below the ribs and a large mass (the swollen spleen) may be felt.
Chronic Anemia. Because of the short lifespan of the sickle red blood cells, the body is often unable to replace red blood cells as quickly as they are destroyed. This causes a particular form of anemia called hemolytic anemia. Most patients with sickle cell disease have a hemoglobin levels of 8 g/dL, much lower than people without sickle cell anemia.

 

Chronic anemia reduces oxygen and increases the demand on the heart to pump more oxygen-bearing blood through the body. Eventually, this can cause the heart to become dangerously enlarged, with an increased risk for heart attack and heart failure.
On occasion, patients may experience what is called an aplastic crisis. This happens when the cells in the bone marrow that are normally trying to make new red blood cells suddenly stop working.

                     What is Sickle Cell Anemia?

http://www.nlm.nih.gov/medlineplus/ency/article/000527.htm

Sickle Cell Anemia (aka Sickle Cell Disease)
Pain Crisis Symptoms
Symptoms usually do not occur until after age 4 months.
Almost all patients with sickle cell anemia have painful episodes (called crises), which can last from hours to days. These crises can cause pain in the bones of the back, the long bones, and the chest.
Some patients have one episode every few years. Others have many episodes per year. The crises can be severe enough to require a hospital stay.
When the anemia becomes more severe, symptoms may include:
• Fatigue
• Paleness
• Rapid heart rate
• Shortness of breath
• Yellowing of the eyes and skin (jaundice)
Younger children with sickle cell anemia have attacks of abdominal pain.
The following symptoms may occur because small blood vessels may become blocked by the abnormal cells:
• Painful and prolonged erection (priapism)
• Poor eyesight or blindness
• Problems with thinking or confusion caused by small strokes
• Ulcers on the lower legs (in adolescents and adults)
Over time, the spleen no longer works. As a result, people with sickle cell anemia may have symptoms of infections such as:
• Bone infection (osteomyelitis)
• Gallbladder infection (cholecystitis)
• Lung infection (pneumonia)
• Urinary tract infection
Other symptoms include:
• Delayed growth and puberty
• Painful joints caused by arthritis
 
Acute conditions are severe and sudden in onset. This could describe anything from a broken bone to an asthma attack. A chronic condition, by contrast is a long-developing syndrome, such as osteoporosis or asthma. Note that osteoporosis, a chronic condition, may cause a broken bone, an acute condition. An acute asthma attack occurs in the midst of the chronic disease of asthma. Acute conditions, such as a first asthma attack, may lead to a chronic syndrome if untreated.