I'm 50, i was laying in bed w my wife and she said I was shaking. I didnt notice but she was sure. Whats up?

We were snuggling and she says why are you shaking? I said i'm not. I focused and actually noticed a very slight vibration or shake...my whole body, very subtle. Then 2 days later I was laying down and noticed it myself. Almost imperceptable but a very slight full body tremor. Any ideas on what this can be?