Make a LOOP function with a delay

Hi there,

I have a query as below which works great and does exactly what I want
it too. It has this form:

SELECT my_function(
field_one,
field_two,
field_three,
field_four
)
FROM my_table
WHERE row_number = 1;

However I want to make it loop and run the function for each row of
my_table. I'd also like to put a delay in it. But I'm not quite sure
how. The pseudo-code would be:

1) Take the first row from the table
2) Run the function with the row number in the WHERE clause
3) Pause for 5 seconds
4) Move to the next row
5) Run the function again
etc... until the whole table is done.

I'd really appreciate some guidance please. I've looked at loops in
the manual but it's a steep learning curve...

Thanks

James