Minecraft Out Of Memory

What I expected to happen was...:
I was in a map (Cops and Robbers 3) and I was just flying.

What actually happened was...:
When I flew out of the building I got the in-game Out Of Memory screen, so I clicked on the button that said "Return to Title Screen" and tried to load the map again. When I clicked on the map I wanted to load it retuned me to the new launcher and gave me this error report:

---- Minecraft Crash Report ----
// I feel sad now :(

Time: 7/4/13 10:34 PM
Description: Updating screen events

java.lang.OutOfMemoryError: unable to create new native thread
	at java.lang.Thread.start0(Native Method)
	at java.lang.Thread.start(Unknown Source)
	at net.minecraft.server.MinecraftServer.v(SourceFile:579)
	at atn.a(SourceFile:1426)
	at avy.e(SourceFile:157)
	at avy.a(SourceFile:122)
	at avv.a(SourceFile:71)
	at avv.d(SourceFile:125)
	at avv.m(SourceFile:109)
	at atn.k(SourceFile:1157)
	at atn.S(SourceFile:662)
	at atn.d(SourceFile:618)
	at net.minecraft.client.main.Main.main(SourceFile:101)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Stacktrace:
	at java.lang.Thread.start0(Native Method)
	at java.lang.Thread.start(Unknown Source)
	at net.minecraft.server.MinecraftServer.v(SourceFile:579)
	at atn.a(SourceFile:1426)
	at avy.e(SourceFile:157)
	at avy.a(SourceFile:122)
	at avv.a(SourceFile:71)
	at avv.d(SourceFile:125)
	at avv.m(SourceFile:109)

-- Affected screen --
Details:
	Screen name: bli
Stacktrace:
	at atn.k(SourceFile:1157)
	at atn.S(SourceFile:662)
	at atn.d(SourceFile:618)
	at net.minecraft.client.main.Main.main(SourceFile:101)