Why do some people fall or shake and others don’t? Does it mean that when you don’t have these signs, you have not received the Holy Spirit?

In answer to your question, there is not anything specific in the scriptures about being slain in the Spirit or these other specific physical manifistations, although we do see evidence of the power of God literally knocking someone down.

For instance, when the Roman guards came to arrest Jesus they were literally knocked backward by just the power of His word:
John 18:6 As soon then as he had said unto them, I am he, they went backward, and fell to the ground. (This is a good reference verse for those who do not realize that Jesus laid down His life for us: no one could not have taken Him except that He allowed it).

There are other places in scripture that indicate an unusual physical reaction to the power of God, just as Saul was knocked down on the road to Damascus. John, in Revelation, fell under the power of God. When the Holy Ghost comes in power our flesh can be overwhelmed by His presence. It does not mean that someone quietly seeking God in private prayer times cannot also experience the same closeness to God as no one cam truly comprehend all of the marvelous ways that God chooses to come in a personal way to His children.

The most important thing is to always seek the Manifestor of these experiences, not the experience itself.

Thank you for your excellent question.

Pastor Brad