The aromatic shrub was present in your very courtyard. When you had a bad cold, your mother made a herbal tea with it. By drinking that hot medicinal tea, you felt your breathing passage opening up and could take fresh air in. If you are a Hindu, you might have found a religious connection too with the plant as it was present in a tray with other objects during many rituals like obeisance to your deceased ancestors.
The shrub we are talking about is nothing but Tulsi or Holy Basil. The scientific name of the plant is Ocimum Tenuiflorum and it belongs to the family of Lamiaceae. Three common varieties of Tulsi seen in Kerala are Rama Tulsi, Krishna tulsi and Karpoora Tulsi. Perhaps, it is the medicinal property of the plant that made people of the ancient era to consider it a sacred plant. The herb is extensively used in Ayurvedic medicines for cough, common cold, head ache,  respiratory and stress related diseases etc are based on the medicinal property of Tulsi.
Medicines extracted from the plant are used for both preventive and curative purposes. Tulsi may be the most prominent medicinal plant involved in the common home-made remedies for cough, stomach ache, head ache, cold etc. It has the potential to lower the blood pressure levels too, so it is used in the Ayurvedic treaments for stress-related ailments too.