Is sedation necessary for sinus lift and 4 implants?

A sinus lift and 4 implants is oral surgery, not general dentistry. Your surgeon has your comfort in mind as well as a realistic understanding of what the surgeries entail. The side effect of nausea and vomiting can be addressed with the anesthesiologist. There are alternative sedatives which may not cause this for you.  No medicine, sedation medicine, is without side effects. 
You trust your surgeon to perform your procedures, trust that he/she has your best interest in mind to create the surgical environment for patient comfort as well as surgical success. 

This kind of procedures are lengthy procedures and it requires comfortable environment for both the patient to be relaxed and calm , and for the doctor himself while performing this procedure and not to deal with patient movements and re positioning on the chair specialy when dealing with such comprehensive procedure of sinus lift and 4 implant placement. Throwing up is most of the time due to nausea caused by sedative medication but  this issue can be controlled by many anti-nausea medications that can take care of that. But again it is preferred but not a must.