Just a caution; for me that was always the intro to a depressive bout. The interest seemed to drain out of things. Stay aware and if it becomes prolonged or deepens you may be a candidate for anti-depressant therapy.

If this includes a negative re-assessment of what you have accomplished or the importance of it be especially cautious. Retrospective ennui is a red flag.

Here's hoping it's just a minor glitch or short term burnout.