Whackload of issues popped up

23:13:46
cfw
Client thread
warn
Skipping bad option: lastServer:
23:14:32
bv
Client thread
warn
Ambiguity between arguments [teleport, destination] and [teleport, targets] with inputs: [Player, 0123, @e, dd12be42-52a9-4a91-a8a1-11c01849e498]
23:14:32
bv
Client thread
warn
Ambiguity between arguments [teleport, location] and [teleport, destination] with inputs: [0.1 -0.5 .9, 0 0 0]
23:14:32
bv
Client thread
warn
Ambiguity between arguments [teleport, location] and [teleport, targets] with inputs: [0.1 -0.5 .9, 0 0 0]
23:14:32
bv
Client thread
warn
Ambiguity between arguments [teleport, targets] and [teleport, destination] with inputs: [Player, 0123, dd12be42-52a9-4a91-a8a1-11c01849e498]
23:14:32
bv
Client thread
warn
Ambiguity between arguments [teleport, targets, location] and [teleport, targets, destination] with inputs: [0.1 -0.5 .9, 0 0 0]
23:14:40
net.minecraft.server.MinecraftServer
Server thread
warn
Can't keep up! Is the server overloaded? Running 2019ms or 40 ticks behind

I can't look around without a laggy screen in singleplayer mode. The game itself (i.e. enemies) still move in realtime.