Hallucinations while half-asleep are a well known phenomenon, so it's very possible.

If you're trying to know for certain, that's harder. You'll have to consider a lot of things. Not all of them are likely, so how much digging you do is dependent on how concerned you are.

Do you live alone? I assume you do, or already asked the people you live with.

Are all your exterior doors and windows locked? Is anything missing or out of place? I think you'd have already noticed if you'd been robbed, but this is easy stuff to rule out.

Do you have functioning Carbon Monoxide detectors? Do you have sleep apnaea? CO can lead to memory loss, sleep apnaea can contribute to sleep paralysis.

Have you seen your door open while half asleep before? If this is recurring, you can do things like place hairs in the door that will fall if it opens.

Have you done a sleep study? This can help determine if your REM cycle is frequently disrupted and if you need something like a CPAP.