I wrote a simple program to get the mouse position using win32api. But I found that sometimes negative values ​​appear. Why is that?

import ctypes
import ctypes.wintypes
import sys

user32 = ctypes.windll.user32
WM_MOUSEMOVE = 0x0200

class POINT(ctypes.Structure):
    _fields_ = [("x", ctypes.c_long), ("y", ctypes.c_long)]

class MSLLHOOKSTRUCT(ctypes.Structure):
    _fields_ = [("pt", POINT), ("mouseData", ctypes.wintypes.DWORD), ("flags", ctypes.wintypes.DWORD), ("time", ctypes.wintypes.DWORD), ("dwExtraInfo", ctypes.c_ulong)]

def showxy(x, y):
    print("x=%d y=%d" % (x, y), end="              r")

def LowLevelMouseProc(nCode, wParam, lParam):
    if nCode == 0:
        if wParam == WM_MOUSEMOVE:
            msl = ctypes.cast(lParam, ctypes.POINTER(MSLLHOOKSTRUCT)).contents
            x = msl.pt.x
            y = msl.pt.y
            showxy(x, y)
        elif wParam == 513:
            print("Left button pressed")
        elif wParam == 0x0204:
            print("Right button pressed")
    return user32.CallNextHookEx(0, nCode, ctypes.wintypes.WPARAM(wParam), ctypes.wintypes.LPARAM(lParam))

def main():
    LRESULT = ctypes.c_long
    MYCFUNC = ctypes.CFUNCTYPE(LRESULT, ctypes.wintypes.INT, ctypes.wintypes.WPARAM, ctypes.wintypes.LPARAM)
    CFIMCP = MYCFUNC(LowLevelMouseProc)
    hook_id = user32.SetWindowsHookExW(14, CFIMCP, None, 0)
    msg = ctypes.wintypes.MSG()
    while user32.GetMessageW(ctypes.byref(msg), None, 0, 0) != 0:
        user32.TranslateMessage(msg)
        user32.DispatchMessageW(msg)

if __name__ == '__main__':
    main()

I only use one monitor. Move the cursor to the screen coordinates and then quickly move it up and down to see negative values.