My DeFi position just showed a 40% loss that disappeared an hour later. What is impermanent loss and why did no one explain this before I put money in POST

The user's DeFi position showed a 40% loss that disappeared an hour later, leaving them confused about impermanent loss. The user had provided liquidity on a DEX two weeks prior and was earning fees before the sudden loss. The loss then decreased to 8% after an hour.