What can be the reason of heaviness in head and eyes after botox application and when will it subside?

Paralysis : Botox paralyzes the muscles on the forehead and around eyes if it was injected there causing this feeling. It could last up to 3 months. You should see your doctor for evaluation.

Common with 1st injx: Theis is a common complaint with the very first injection and may be due to a combination of lack of familiarity with the sensations of an immobile forward and lymphatic stasis. Generall this will resolve over a two week period. The only concern is if your eyelid covers your pupil = blepharoptosis weir which you should see your injecting physician.

Swelling: Often Botox is mixed with Normal Saline and multiple injections can lead to some swelling around the forehead and eyes causing a sensation of "heaviness" this usually happens on the day of the injections and resolve in a couple days.