Age gap issues??

I'm in need of some advice... 

My eldest is 16months and my youngest is just 12weeks but I found out I'm pregnant again even only after having unprotected s** once.

Friends and family keep telling me it's dangerous?? that my health could be at serious risk?? And some have said It could kill me or the baby??

I don't know if this is just to scare me but I just wanted some advise from other mummy's that have had their children close in age? Wether what I'm being told us just silly or I have got something to worry about??