Levitation is a harmful (negative) status effect in Minecraft Java Edition 1.21.
minecraft:levitation
Give Levitation II for 60 seconds (Java Edition 1.13+; duration in seconds, then amplifier where 0 = level I):
Remove the effect from the nearest player:
Levitation lifts you into the air against your will, and when it wears off, gravity collects the debt with fall damage.
Shulker projectiles in End cities apply Levitation for about ten seconds. There is no potion and no way to inflict it on yourself in survival; it is purely a shulker hazard.
Being levitated high over the End city walkways is lethal on landing, so carry slow falling, ender pearls, or a water bucket to cancel the drop. Blocking shulker bullets with a shield prevents the effect entirely.
The effect ID for Levitation is minecraft:levitation. Java Edition 1.13+ /effect commands use this namespaced form. On Java 1.12.2 and earlier the numerical ID was 25.
Run /effect give @p minecraft:levitation 60 1 to get Levitation II for 60 seconds. The first number is the duration in seconds; the second is the amplifier (0 = level I, 1 = level II). Remove it with /effect clear @p minecraft:levitation.
Levitation is a harmful (negative) status effect in Minecraft Java Edition, based on its registry category (harmful).
Drink milk to clear it, or negate the fall with Slow Falling, an ender pearl thrown at a wall, or a water bucket placed before landing. Blocking the shulker projectile with a shield avoids the effect altogether.
Shulker bullets, fired by shulkers in End cities. The homing projectiles apply Levitation on hit unless blocked with a shield or dodged.