playerdownimg = {} --add this where you have your declarations
reviving = {} --this, too

addhook("hit","RotU.hit_hook")
function RotU.hit_hook(id,source,weapon,hpdmg,apdmg,rawdmg)
	if player(id,"team") == 2 and player(source,"team") == 1 then
		if lives[id] then
			health[id] = health[id] - 25
		end
		if health[id] <= 10 then
			if not onced[id] then
				RotU_msg("©255000255"..player(id,"name").." is down!")
				playerdownimg[id]=image("gfx/Reign of the Undead/rotu_help_img.png",id+200)
				lives[id] = false
				pdown[id] = true
				parse("speedmod "..id.." -100")
				onced[id] = false
			end
		end
	end
end

addhook("use","RotU.use_hook")
function RotU.use_hook(id)
	local pos={player(id,"tilex"),player(id,"tiley")}
	for _,oid in pairs(player(0,"table")) do
		if pdown[oid] then
			if not reviving[id] then
				if pos[1]==player(oid,"tilex") and pos[2]==player(oid,"tiley") then
					timer(5000,"RotU.revive",oid)
					reviving[id]=oid
				end
			elseif reviving[id]==oid then
				freetimer("RotU.revive",oid)
				reviving[id]=nil
			end
		end
	end		
end

addhook("move","RotU.move_hook")
function RotU.move_hook(id)
	if reviving[id] then
		freetimer("RotU.revive",reviving[id])
		reviving[id]=nil
	end
end

function RotU.revive(id)
	id=tonumber(id)
	if pdown[id] then
		freeimage(playerdownimg[id])
		pdown[id]=false
		lives[id]=true --I guess?
		onced[id]=true --I guess?
	end
end