During yesterday's sleep period there were no colors for hours.

I'd like to get going after the next sleep period.

By the time I tracked everything down it was well into sleep period.

And my sleep period was not even ship's night.

Following a sleep period, the crews prepared for another day of joint activity.

You were, of course, watched all afternoon during your sleep period?

When they were through, it was nearing time for a sleep period.

Time pattern Does the hunger occur during the sleep period?

They had only been in space for ten sleep periods.

There was no door, although a forcefield came down during sleep period.