Highly unlikely

For one, every time we see the Q, the Q aren't too shy to announce who/what they are, and Nagilum never does so. Also, all the Q always emulate human(-oid)s, and Nagilum doesn't do that either.

Also note that the Q are far from the only sheer-omnipotent beings in space. For instance the Douwd (as seen in TNG S3E03).

Highly unlikely

For one, every time we see the Q, the Q aren't too shy to announce who/what they are, and Nagilum never does so. Also, all the Q always emulate human(-oid)s, and Nagilum doesn't do that either.

Also note that the Q are far from the only sheer-omnipotent beings in space. For instance the Douwd (as seen in TNG S3E03) are pretty powerful too. Nagilum can simply be a member of an unknown, to our minds quite powerful species. Or just a completely singular being.

Highly unlikely

For one, every time we see the Q, the Q aren't too shy to announce who/what they are, and Nagilum never does so. Also, all the Q always emulate human(-oid)s, and Nagilum doesn't do that either.

Also note that the Q are far from the only sheer-omnipotent beings in space. For instance the Douwd (as ssen in TNG S3E03).

Highly unlikely

For one, every time we see the Q, the Q aren't too shy to announce who/what they are, and Nagilum never does so. Also, all the Q always emulate human(-oid)s, and Nagilum doesn't do that either.

Also note that the Q are far from the only sheer-omnipotent beings in space. For instance the Douwd (as seen in TNG S3E03).