Don't panic. This is a really tough thing to hear.
My two have dyslexia and dyspraxia, and when first diagnosed it took a long time for me to get my head around the idea that I had children with special needs, as opposed to special children with needs.
Despite the news they remain the same kids they were yesterday - just as charming and loveable.
I thought I did not have any expectations about what my kids would do or achieve in life. I discovered I had a load of preconceptions (that they would love curling up with a book as much as I do, for example). It is tough, but you learn your kids are individuals, not you.
Firstly, go to your GP and get a full assessment. Also, start getting your DS statemented, or at least get advice about whether that is appropriate.
My neighbour's son had no verbal language at all aged 4 and still has marked speech and language delay, but is coping at well at mainstream school with 35 hours a week support. He has friends and was voted onto the school council as the class rep, so clearly he is chatting away just fine.
Your school should have SENCO who can help you with this, otherwise your GP should be able to refer you to a paediatrician, or community paediatrician.
Take care.