Hospitals across the county are facing "significant pressure" as the bank holiday approaches.
University Hospitals Sussex NHS Foundation Trust said that hospitals are extremely busy and that people should only attend A&E for serious or life-threatening cases.
For less urgent situations, people have been advised to consider alternatives such as NHS 111 and minor injury units.
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Relatives of patients in hospital who are ready to be discharged have also been asked to try to arrange picking them up as soon as possible. This will help free up space for people needing immediate care.
A spokesman for the trust said: "To help relieve pressure on our hospitals, staff are working hard to get patients who are ready to go home quickly and safely.
"If you have a family member or loved one ready to leave hospital, please speak to ward staff about how you can help."
A spokesman for NHS Sussex said: "NHS services in Sussex are currently very busy and we expect this to continue into the bank holiday and half term holiday.
"Please help us help you by choosing the right service for your needs."
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