The festival of lights usually bring darkness into the lives of animals.
Gentle and friendly, Sultan is a gorgeous brown Labrador. But come Diwali and the high decibel firecrackers make him unpredictable and irritable.
Reshma Singh, Sultan's owner, said: "He is not himself during Diwali. Two to three days preceding the festival, he becomes restless and moody. He doesn't eat well, barks endlessly and constantly wants to remain indoors, under the bed or table for fear of loud firecrackers," Singh says.
"Knowing what an adorable thing he is, this helplessness and fear in him really disturbs us all. We try and shield him away from the loud noise," she added.
Altered behaviour, irritability and changed eating patterns among animals are a common Diwali feature, according to pet owners and veterinary doctors.
Dogs, with an acute sense of hearing - a range of 20-40,000 Hz as compared to 20-20,000 Hz for humans - are the worst affected during the festival, which is to be celebrated Friday.
Daily admissions at the Jeevashram Veterinary Hospital in south Delhi, for instance, rise by up to 10 percent a few days before and after the festival.
According to veterinary doctor M. Mishra, in times like Diwali when there is commotion everywhere, animals need to be comforted.
"It is essential that owners be near their pets, comfort and reassure them. For bigger animals like dogs, there is always the option of sedating them, but for smaller ones, like birds, the only way is to keep them as far away from the noise as possible," Mishra said.
Doctors also suggest that birds can be given their feed and then their cages covered with a dark cloth by afternoon so that, thinking it's night already, they fall off to sleep before the crackers start bursting in the evening.
But it's not just noise that affects the animals.
The smoke in the air, just like it adversely affects human beings, also affects animals. It can aggravate respiratory tract diseases, cause eye allergies and bring on a skin rash.
Flat-nosed dogs like pugs and boxers are worse off when it comes to tackling air pollution.
Sunita Sharma, who owns three cats, said a visit to the veterinary doctor has become a must after Diwali.
"That's because my cats will suffer from something or the other during this season. Either their eyes will be sore or they can't breathe well or they will break into a rash...you can't help feel sorry for these poor things who are so helpless," Sharma said.
But not all animals are lucky like Singh's Sultan and Sharma's cats. For thousands of stray animals, Diwali is an agonising period with virtually no one to even feel for them, let alone rescue them.
An animal welfare organisation, Circle of Animal Lovers (CAL), is however doing its bit for helpless animals on the Delhi roads.
Irani Mukherjee, the founder of CAL, said: "Our sensitising campaign will start Wednesday, two days ahead of Diwali. Our volunteers will go to Jantar Mantar and distribute pamphlets and hold banners telling people that a joyous festival like Diwali should not become a nightmare for helpless and innocent animals.
"Diwali is the festival of lights, why create a ruckus with firecrackers? Not only animals, there are so many cases of people getting injured or burnt because of firecrackers," Mukherjee said.
On Diwali, CAL will have two vehicles stationed in south Delhi's Saket area, ready to rescue any stray animal that might have been injured in the festivities.
"Anyone can give us a call at 9899453221/9873267037 and inform us about an injured animal and we will get him to our shelter where he will be treated for two days before being left from where he was rescued," Mukherjee told IANS.
"I also request people not to shoo away animals like dogs who might enter their premises during this time. They are petrified of the noise and are simply looking for some shelter.
"It's not unusual to even have animals suffer from cardiac arrest because of firecrackers," she said.