Hello, I have gone through your query and understand your concern. As your pain decreases on taking pain killers with the history of rode on roller coaster this may be due to pulled muscle in your chest wall. This can be surprisingly painful, but with rest, the pain should ease and the muscle will heal with time. There are various muscles that run around and between the ribs to help the rib cage to move during breathing. If a muscle is strained, there has been stretching or tearing of muscle fibres, often because the muscle has been stretched beyond its limits. This may cause your chest pain usually worse on movement and on breathing in.Increase in pain while up in stairs further due to the muscle strain in the chest wall. You need to take some rest and pain killers like ibuprofen. Hope this helps. Please write back for further queries. Wishing you good health.