The ruling in the PHB says that the only downside to standing up from being prone is that you lose half your movement. This makes the shove action somewhat underwhelming, as well as a bunch of spells and abilities (specifically monster abilities).
Is it an action to get out of prone?
You can drop prone without using any of your speed. Standing up takes more effort; doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to stand up.
How much movement does it take to stand up from prone?
For example, if your speed is 30 feet, you must spend 15 feet of movement to stand up. Bonuses/penalties to speed apply to your speeds in general, unless the text specifies walking, flying, etc. Thus standing up from prone would cost movement equal to half all of your speeds.
How many movement speeds do you have before standing up?
The math works out as well: before standing up (with 30′ walking/60′ flying) you had an effective maximum movement of 60′ (since using multiple movements means that essentially you are capped at your largest speed). After standing up (15’/30′) you have an effective maximum movement of 30′, so half of the original.
What does it mean to be prone with multiple movement speeds?
The grappled condition reduces any speed you have to 0. If you have a flying speed, it’s now 0, and you fall unless you’re hovering. So clearly, when the game says speed they are referring to all of your speeds. Thus “an amount of movement equal to half your speed” is also referring to all of your speeds.
Can You Drop prone without using your speed?
Since this is clearly a rules hole, arguments could be made for other readings. You can drop prone without using any of your speed. Standing up takes more effort; doing so costs an amount of movement equal to half your speed. For example, if your speed is 30 feet, you must spend 15 feet of movement to stand up.
