int Switch5 = ProcessMemoryReaderApi.GetKeyState(0xA1);
    if ((Switch5 & 0x8000) != 0)
    {
        act = !act;
        if (act)
        Console.WriteLine("true");
        else Console.WriteLine("false");
    }

private bool _IAmWorking;
public void KeyEventHandler(EventArgs event)
{
    if (_IAmWorking) return;
    _IAmWorking = true;

    ......

    _IAmWorking = false;
}