I wonder if any of you can enlighten me about the rules/principles of shielding?

I understand that there can't be any gaps or slots when shielding and in effect you need to be in a sealed (shielded) unit. But I am also confused about if you then create EMFs within this unit by using something electrical (I hardly use anything but Im reliant on an electric wheelchair). Ive heard that this can worsen the sensitivity symptoms by creating EMFs that bounce around the room?

Also has anyone had any negative experiences of shielding whereby it reflects the bodys own EMFs back at them?

Thank you.