I feel my chest becoming very heavy when I lie down to sleep. This has worsened over the past few weeks. When I am standing up or sitting down during the day I sometimes feel like I am short of breath, even when I am not physically moving whatsoever, but that feeling is manageable and it does not last very long. The real problem is when I lie down on my back -- I feel like there is a 100lb sack being push against my chest and it's hard to breath and my heart beats faster.
The chest pressure you are dealing with may be anxiety/stress related. When you are feeling overly anxious, your heart rate might quicken, you may have sweaty palms, experience shaking or chest pain. Your blood pressure may also go up. But once the situation resolves itself and the anxiety provoking moment is over, your body returns to normal. Your heart rate slows, the chest pain disappears and your blood pressure lowers.
Chest pains come in many sizes and shapes. They might be experienced as fullness, heaviness, an aching, a drawing, burning, squeezing, fluttering, and many, many other ways. One very common presentation for chest pain is that of a sharp chest pain. Sharp can be perceived as stabbing, like a needle or a knife is piercing the skin. This is a very common chest pain and doesn't necessarily mean anything serious.
Nonetheless, any chest pain could be serious - so it's best just to check it out with your doctor and eliminate anything serious.