This happened to me several years ago. Perhaps while trying to use a “Fn” key to change the volume on my laptop, I disabled my touchpad by pressing the wrong button. For weeks I didn’t know what the issue was, which wasn’t helped by the touchpad function icon on my keyboard looking ''just'' like a monitor icon, and it took me a while to realise that maybe it was in fact a touchpad icon.
While holding the “Fn” key, press every function button (the “F” keys) with a symbol on it that looks like it could be your touchpad to see if it switches back on. (Bear in mind, you might turn off your screen this way, so just press that button again if that happens.)