Brief Answer:
Hypnic jerks more likely

Detailed Answer:
I read your question carefully and I understand your concern.

Those shaking episodes in isolation are too little to make a diagnosis of RLS. RLS has other more prominent symptoms necessary to make the diagnosis, such as the urge to move the legs with an unpleasant sensation unless you do, which is more pronounced in the evening, during inactivity, relieved at least partially by moving.
If you haven't such an urge with unpleasant sensation, relieved by movement then RLS diagnosis can't be made. RLS occurs while awake as well as while sleeping.

There is the possibility of PLMS (periodic limb movement disorder), where there are repeated involuntary movements during sleep, but usually the patient doesn't wake up, doesn't remember them, accompanied by sleepiness and fatigue during the day. So still unlikely, certainly not a diagnosis which can't be made without confirming it with tests like polysomnography.

Judging by your description my opinion is that it is more likely that those episodes are hypnic jerks or sleep starts as they are otherwise called. They are very common, about 70% of people experience them at least once, some more frequently than others. Cause is not well known, one hypothesis is it may be a phenomenon during transition between sleep stages, another hypothesis is that as muscles lose their tone the brain falsely perceives that as if the patient is falling and leads to muscle contraction.
They are often related to stress and anxiety, exercising in the evening, consumption of caffeine or energy drinks, alcohol use, exhaustion and fatigue. So in order to cope with them avoiding these factors and relaxation exercises would be recommended.

I remain at your disposal for other questions.

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