Currently, when a character is knocked unconscious and needs to start making Death Saves, if they are helped up from a character, they then lose their next action when their turn comes up. In D&D 5e, getting up from being prone takes half of your movement and not an action, and there is no such restriction for revived player characters. This creates a double punish because you always lose your next turn, and if your turn was skipped from being unconscious then you have essentially lost 2 turns. This creates a death spiral where recovering from a character being knocked unconscious becomes very difficult and not cost effective in terms of actions used, since you need another character to spend an action to bring the downed character back up.

I'm not sure if it also costs an action to get up from being prone when you are knocked prone but still conscious.

Either way, getting up after being knocked unconscious should not spend your next action. It's very frustrating to be knocked out and then essentially lose 2 actions (the helper and the downed character) to get them back into the action at 1 HP, and they usually just get downed immediately before they can do anything. It should use D&D 5e's rules for standing up after being prone.