This is a rookie Advaita question that so many people ask when first introduced with Advaita.
Why isn't everybodies' experience not the same and why doesn't everybody experience everything that others are experiencing?
This has been answered so many times again and again the simple short technical answer is that all experience happens on the five kosha level, not on the Atma level.
Did you get it? If not continue to read for further explanation.
The pain you are talking about mainly happens in Annamya, Manomaya and Pranamaya koshas. These koshas are different for different people. The Atma which is same is beyond all these, koshas. Excerpt from Nirvana Shatkam
न वा सप्तधातुः न वा पञ्चकोशः ।
2.2: Neither am I the Seven Ingredients (of the Body), nor the Five Sheaths (of the Body)
चिदानन्दरूपः शिवोऽहम् शिवोऽहम् ॥२॥
2.4: I am the Ever Pure Blissful Consciousness; I am Shiva, I am Shiva, The Ever Pure Blissful Consciousness.
The Thing which is reffered to as Sacchidananda Shiva or Brahman or Atman is beyond the five koshas.
There is also the problem of the word consciousness, it is used differently in English and differently while translating Sanskrit to English, especially Advaita works.
In English, you can say
someone was unconscious. This is a proper usage. What it means is someone is not awake. But the statement
someone was unconscious is totally wrong according to Sanskrit and Advaita, as someone can never be unconscious as they themselves are consciousness. Do you see the problem? The consciousness word in English is equivalent to Jagrut state which is also reffered to as Vijnana or Chidabhasa. But Sanskrit consciousness is reffering to Chit, which is always present.
This question is coming because the nature of Atma is not understood properly. You are confusing Chit which is one true Atman with Chidabhasa or multiple reflections of the Atman in multiple bodies.
The experience of pain happens mainly at first four koshas. It doesn't even touch Atman. The memory of different experiences is stored in Manomaya kosha which is different for different people. According to Advaita each person has his or her own five koshas. What is common between all humans is the consciousness(or Chit) which is behind all these koshas.
This is a little sophisticated concept, let me illustrate the same idea with a classical example.
This is famous example in Advaita.
Just as the one, single Sun in the sky gets its many reflections in
various vessels of water, so Thou, O Lord, art (variously) reflected
in different minds. Shiva Gita 7.34
Now imagine that all the pots are Annamaya kosha and water inside is Manomaya kosha etc. There is one Sun in the sky, whose reflection is there in all the pots. These reflections are called Chitbhasa, while the Sun is the real Chit in this example. If you see, it will be like there are hundreds of Suns, one in each pot, one big, one small, one wavy and one coloured. But all these differences are because of pot and contents of pot.
You, say pricking your hand with a pin and asking why the other person doesn't feel pain is like disturbing water in one pot and seeing the Sun's reflection in that pot getting wavy and asking, why aren't the other Suns in other pots not getting wavy, if they all share the same Sun?
Do you see the problem? The actual thing is never touched. Atma is never touched by your pain and suffering. It simply watches like the Sun simply sheds light on all pots.