Getting ready to get a deep cleaning on all my back teeth only,very scared!! will i bleed a lot, will i need antibiotics, scared infection can spread?

Don't be scared: If you require a deep cleaning you have an inflammatory/infection gum disease problem. Appropriate treatment has been scheduled. Failure to proceed with treatment will only allow infection to worsen and spread. There will be some bleeding, but not a lot. You will not need antibiotics unless you have had heart surgery. DO NOT CANCEL YOUR APPOINTMENT.