Whether a person is disabled per the rules and regulations of the social security disability program is determined by three things: 1) He or she must have a severe impairment; 2) the person cannot perform work in a substantial way due to her medical condition; and 3) the medical condition must have lasted or be expected to last at least one year.
The SSA has a list of conditions that are so severe, that they automatically qualify you for disability benefits. These are called Compassionate Allowances and include acute leukemia and kidney cancer, for example. (see, https://www.ssa.gov/compassionateallowances/) There are also 14 “listed impairments” that, if the condition meets the medical criteria, results in disability automatically. However, most conditions vary greatly and therefore it is difficult to meet all the requirements. In the social security disability world, you either are disabled or you are not. In other words, if a person is 50% disabled, they will not be eligible for 50% of benefits. The person must have a condition that is severe enough to affect their ability to work and it must last or be expected to last for at least a year.
If a person has more than one condition, the SSA considers the totality of the way in which they affect that individual. If the combination of impairments severely limits the person, then they will be found disabled. Many people have both physical and mental conditions that affect their ability to work, for example. Ask your local social security disability lawyer to help you determine if you may be eligible for benefits.