The 4th house in any birth chart has various significations such as house, vehicles, peace of mind, mother etc. Generally most astrologers look at the 4th house with a view to deciphering whether the native will be blessed with comforts and vehicles. A significant aspect of 4th house is attributable to mental peace and inner purity. Generally 6th lord in 4 goes under the name "Kapata Yoga" or yoga for becoming a thief. It generally refers to lack of cohesion in thought, word and deed. Malefics in 4 or aspecting the 4th house make a person deceitful in all dealings and this in turn deprives the native of peace of mind.
Mental stress is caused if the 4th house is aspected by malefics. In medical astrology malefics in 4 can lead to cardiac problems.
To understand the full features of 4th house we need to look at Moon, Mars and Mercury. Moon is the karaka for mother. So Moon and the 4th lord both afflicted lead to deprivation of maternal happiness. The greatest source of joy and comfort in this world is a loving mother. There is a saying that when a person is born, God also designates a "Guardian Angel" to look after that person. We know that a loving mother is the physical equivalent of that Guardian Angel. When Moon is afflicted, one's mother will not be of any help to the native. So that could be one causative factor for mental anguish. According to Dr. B.V. Raman, "Insanity or madness will not be present unless the Moon and Mercury are involved in heavy afflictions". This is because Moon rules the mind and Mercury rules certain emotions like sense of humour.
Mars is "Bhoomi Karaka", if Mars is afflicted in the 4th, one will be bereft of happiness and also property related dealings will suffer.
To conclude, one will be blessed with peace of mind, happiness and comforts if the 4th house and 4th lord are free of any blamish of any sort. Benefics such as Jupiter or Venus aspecting the 4th house would also give a person, cheerfulness, joy and enthusiasm.Today most doctors all over the world assess a person's state of mind before writing out a prescription.Stress is now considered as a serious causative factor in many psychosomatic disorders.So all afflictions to the 4th need to be reckoned before diagnosis of such disorders is made.