I wasn't sure but i did some reasearch .
Apparently , it is normal for rabbits to shake occasionaly , especially during sleep .
Although shaking while laying down is a sign of illness .
Yours sounds like trembling , apparently this is a gentle quivering motion that’s like a vibration.
Its normal during sleep , if your rabbit is pleased , dis-pleasured , hiccuping and recovering from being scared .
Apparently , not caused any of the above , it can be caused by
Overheating and heatstroke.
Eating or sniffing something poisonous.
Parasite infections, especially E. Cuniculi and Ear Mites.
Bacterial infections.
Strokes.
Gastrointestinal stasis.
End of life approaching, such as muscle tremors.
Apparently these create additional symptoms , is he showing other signs ?
Apparenty , not allowing to be touched , teeth grinding ,bloated stomach , flattened ears ,
cold ears , refusing food and water , falling over and clumsyness and breathing heavy , acompanied by shaking can or is a medical emergency .
I would get to vet asap .
It also says they shake when in pain .