How do I make a Python plug-in for Hexchat thread-safe?

I tried to write a simple Python plug-in for the Hexchat IRC client. However, it seems it is not thread-safe and causes that Hexchat crashes.

__module_name__ = "Demo"
__module_version__ = "1.0"
__module_description__ = "Demo plug-in"
import hexchat
from threading import Thread
from time import sleep
def sleep10seconds():
    hexchat.prnt("before sleep")
    sleep(10)
    hexchat.prnt("sleep end")
    hexchat.command("server " + hexchat.get_info("host"))
    return
# This function is called when a "disconnected" print event was found
def disconnected_cb(word, word_eol, userdata):
    # The sleep() needs to run in a separate thread. Otherwise, the UI
    # freezes for the time of the sleep()
    myThread = Thread(target=sleep10seconds)
    myThread.start()
    return hexchat.EAT_NONE
hexchat.command("discon")
hexchat.command("server " + hexchat.get_info("host"))
hexchat.hook_print("Disconnected", disconnected_cb)

I read some articles about thread safety, but I'm not a developer. I couldn't figure out what I need to change. Can you please help me? Thanks.