The following are all equivalent to the original implication:
I am asleep if I dream.
I dream only if I am asleep.
In order to dream, I must be asleep.
To dream, it is necessary that I am asleep.
To be asleep, it is sufficient to dream.
I am not dreaming unless I am asleep.
The following are equivalent to the converse (if I am asleep, then I dream):
I dream if I am asleep.
I am asleep only if I dream.
It is necessary that I dream in order to be asleep.
It is sufficient that I be asleep in order to dream.
If I don't dream, then I'm not asleep.