This fluid collection is called a seroma. Drains may be used to reduce this risk. Bleeding is uncommon but can require urgent re-operation. If blood collects at the site of surgery it is called a hematoma and may need removal with a needle or by surgery. Drains may be used to reduce this risk.
Infection is rare but can be a serious problem.
For this reason many surgeons use antibiotics around the time of surgery. Numbness is due to the division of small skin nerves during surgery. It is inevitable but in most cases sensation will return but may take up to a year. In rare cases permanent loss of feeling to the skin may occur. In some cases this can be painful due to clumps of scar tissue collecting around the end of cut nerves, called neuromas.