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.
Causes of Heart Palpitations. Many things can cause heart palpitations. In the vast majority of cases, the cause is either related to your heart or is unknown. Non-heart-related causes of palpitations include: 1  Strong emotions such as anxiety, fear, or stress; palpitations often occur during panic attacks.2  Vigorous physical activity.. Heart palpitations are a feeling that your heart is beating too hard or too fast, skipping a beat, or fluttering. You may notice heart palpitations in your chest, throat, or neck. Heart palpitations can be bothersome or frightening.