My 4-week-old autoflower seedling starts the day looking normal when I turn on the light. During the course of the day, the newest leaves in the center gradually become more erect, ending the day nearly vertical. Sometime late in the evening, the older fan leaves begin to droop as if needing water. I turn off the light after 16-18 hours, and in the morning, all the leaves have returned to normal appearance. This has now happened several days in a row. Any suggestions as to what's going on? Thanks!