small period of time

There are two main possibilities and there would be more if you gave some of the contact: This is being said to a person that sleeps a lot, "when you were awake... (this is an unfinished thought by the way.. We do not know what the person will say about the time the other person was awake.) or This is an unfinished thought about someones life. It would be like saying "during the few years of eternity that you lived... (and we still do not know the rest of the thought or the rest of the statement.)

It is an event that happened for a short time. The person who saw this even happen is focusing on that event, trying to look into the window of that space of time and keeping that memory in their mind. That person looking into the window is trying to learn all they can from that view they witnessed.

short term OR short time