There ara various types of jellyfish. On the other hand, human reaction varies as well.
I know a lady who had a jellyfish touced her neck, That lady was very allergic and her neck swelled externally and internally. Ended up in intensive care for some time but she survived.
Generally speaking. Gulf sea is safe. Would recommend wearning suitable beach shoes all the time. You cannot tell what would be hidden under the sand.

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