I'm finding that any disturbances to falling asleep in the 30-60 minute window make my sleep.....disturbed.
For example, just moved into our new place and have pretty much gotten settled in except my boy hasn't quite gotten it that he'll be sleeping in his bed now. Raised a big stink and needless to say sleep was a problem that night.
On the other hand, if I'm really tired like last night, I sleep deeply even if I gotta get up to pee. Today I feel very sharp whereas after the night described above I was groggy, even punchy, all day long.
After a night of disturbed sleep I'm thinking that NOT taking ZMA the next night might work better for me.
"Lack of sleep makes cowards of us all."