This one I don't know anything about... check with doc/pharmacist! I have never taken sleeping pills or dilantin specifically so I pull a zero on this question. I definitely have some insomnia issues either drug induced or b/c of physical discomfort but have always chosen to deal with it in other ways than adding further medications because I take so many AED's already.

What Jeffrey said....
Some people can take things and others like me (unfortunately!) find that multiple medications will lower their seizure threshold!
Always check with the doc! I have also found that sometimes the pharmacist knows things that a general practitioner does not. After getting sick (seizure) on a couple of antibiotics. etc. and then finding out after the fact from the epileptologist that I should not have had it prescribed to me, I started always double checking prescriptions for "regular" illnesses with the pharmacist before taking them.
Fortunately, I don't get sick often....because the list is long.

My doctor always warned me not to - but one night I did. Got into bed. Seconds later, I wasn’t yet sleeping, but I was DEEP dreaming. It was pretty incredible. Everyone here can close their eyes and imagine a certain place, certain people. I closed my eyes, got into bed. Seconds later I was in another world. Look it up on the internet. You’ll find different stories, from different people. And that’s why the doctors alway say stay away when it comes to Dilantin and sleeping pills.

It depends on the sleep medication. Dilantin and a sleep medication called phenytoin can cause dizziness, drowsiness, confusion and concentration problems.
I am also on Dilantin and I was prescribed Trazodone for sleep. Trazodone is an anxiety drug but works well for insomnia too.
Consulting with your neurologist is very important.

Good question to ask Neurologist? I became allergic to DPH. Check first🧑