Temperatures during summer can be a bit suffocating if you are not used to it. It is not common to have more than 35ºC during the day but possible. At night, it goes down to around 20ºC in the very early morning but most flats don't have enough time to cool down. The mediterranean sea makes sure the humidity is high all day and night every day. Having A/C where you are staying is the safest bet if you don't have experience with heat. Fans and dehumidifiers can help too. Keep in mind isolation in flats is not the best in older buildings.