I would guess that too. Adderall and Ritalin-type drugs are stimulants, so is nicotine. So it stands to reason that they were probably working together and now the nic dosage is different. Sorry I cant vote, though, don't take it.
Now that I think of it, though, the PG (in non and low nic form even) made me feel foggy-headed, VG does not. Don't know if that helps or applies. Maybe its PG-related, not nic.