Most unusual - allergy
to antihistamine tablet. However, such things can occasionally happen particularly due to the other excipients in the tablet like phenylephrine
The important thing is to make sure that there is no other cause (like you excluded pregnancy!), such as thyroid disorder
especially if this was happening before.
If you have taken any antibiotics along with Nyquil, then it will be important to consider whether the antibiotics had any role in the symptoms.
It is best you stop the nyquil and switch to something like levocetirizine
. Most cold symptoms are due to viruses, so a NSAID or paracetamol
with levocetirizine should suffice.