How can I check if a form is loaded or not?

Reason for wanting to do this:
I have a button on a worksheet which displays a form. I use
form.show to do this. It takes a long time to load as there is
a lot to do in the initialization.

There is a button the on form that says "exit" but it only hides
the form. If the user then clicks the worksheet button again the
form is displayed very fast as it only has to be unhidden.

There is one condition which can happen which would mean
I want to unload the form. If I use unload.form and the form
is loaded and either hidden or not, it unloads fast. If it is not
loaded it then loads (which takes AGES) then unloads.

I would like to only unload it if it is loaded but cannot work out
how to do check.

TIA.

Chrissy