[SMHarman]

In a recession demand for goods and services falls.
In retail because people want to save more or because other costs have gone up giving less disposable income, these costs could be their mortgage payment because of rising interest rates or could be petrol, energy costs (electricity and gas), commuting etc. Also as companies realise this is occurring salary increases are likely to be low or none again reducing the available disposible income.

At a company level recession means there are less people buying the goods or services the company makes leading to cutbacks in workforce and more significantly a reduction in capital expenditure for the future either in research and development or buying new machinery or general expansion, again leading to a reduction in purchasing from their suppliers.

This keeps going through the entire purchasing chain creating a vicious circle that is difficult to then escape from.