The Ark/Chest
Scholars have said that seeing oneself in a coffin may indicate attaining power and high status if one is deserving, or it could suggest fear of an enemy followed by relief and salvation after a period. This dream might also signify the return of an absent person. If one sees themselves on a coffin, it could point to involvement in a will or a dispute, leading to victory and achieving one's desired goals.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam
Note: These are traditional scholarly interpretations (ijtihad) drawn from a specific classical source — not a binding religious ruling, fortune-telling, or a prediction of the future.