Goldfish hides behind plant

I have just got a small telescope eye goldfish. It has been in the
tank for a little more than a day. It is fine and swimming around
until this evening, when it got behind some plant at one corner of the
tank and settled down there at the bottom. When someone walked pass or
when I looked, it would swim out and around. But later, it would swim
back and sat at that corner.

Is this normal behaviour? Or does it suggest something that I should
be concerned about. I guess I will monitor it and see if it swims out
in the day time.

The first night, it "sleeps" near the top of the water around the
corner of the tank where the power filter is.

There is no other fish in the tank at the moment.

Thanks,
Petre