Depression occur's because of numerous different thing's from it being a chemical deficiency to entirely situational.
So firstly I would take what your friend say's lightly because only a psychiatrist can say if your depression is chronic etc. However depending on your diagnosis and his diagnosis he may be able to make some generalisation in particular if he has been diagnosed as suffering from dysthmia as this is a form of chronic depression.
To have depression for 4/5 year's it is more than simply a one off incident and as Katherine say's
Originally Posted by ~longing~tears~
Whether its chronic, recurring, whatever, its getting the right treatment that matters.
and that treatment should be made for you and fit your circumstances.
If you are still worried and don't want to ask your dr. maybe ask him to say why he say's that you don't have chronic depression his answer will hopefully explain it.
Look after you