SLEEP in posgresql

Hi,

I have a while loop and I want to re-iterate after every 't' seconds.
I was reading up on the postgresql documentation that says pg_sleep(t) should be handy.
However i doesn't work.

Instead of that, I re-engineered my while loop in the stored procedure as follows.

while  a=b loop
 --do something
select pg_sleep(5);
end loop

I doubt this would work because when I try to run
SELECT pg_sleep(5) stand alone, it throws error.

I was wondering how to implement the SLEEP functionality here.

Thanks,
~Jas