Yes, it's common for traders to feel like they've lost their expertise from time to time. This can happen for several reasons, such as taking a break from trading, experiencing a string of losses, or encountering new and unfamiliar market conditions. When traders feel like they've lost their expertise, it can lead to feelings of frustration and self-doubt.
However, it's important to remember that expertise in trading is not a fixed state. It's an ongoing process that requires continuous learning, adaptation, and refinement. Even the most experienced traders can face challenges and setbacks in their trading journey.