Some nebulae create their own light, which sometimes has a fluorescent appearance, while others only reflect the light from nearby stars. Nebulae are often seen around dying stars, and it's thought they may be a natural process that occurs when a star is nearing the end of its life. Nebulae resemble thin clouds that have less atoms per cubic inch than a cloud of smoke.
When there is not enough thyroid hormone, neither the heart nor the blood vessels can function normally. In hypothyroidism, the reduced level of thyroid hormone causes the heart muscle to pump less vigorously, and eventually to become weakened. In addition, the heart muscle cannot fully relax after each heart beat.
Palpitations can occur for a variety of reasons unrelated to heart disease. These include: 1  Overexertion. 2  Stress. 3  Caffeine, alcohol, tobacco, or diet pills. 4  Overactive thyroid. 5  Hormone changes associated with menstruation, pregnancy, or menopause. 6  Low blood pressure. 7  Heart disease or abnormal heart valves.