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.
The following conditions can also sometimes cause heart palpitations: 1  an overactive thyroid (hyperthyroidism) â where the thyroid gland produces too much of the thyroid hormones. 2  a low blood sugar level (hypoglycaemia) â this is most commonly associated with diabetes. 3  anaemia â a reduced number of red blood cells.