A PC and its appendages is a horrendous radio squawk-box and should be kept away from anything RFI-sensitive. The FCC 'must not cause harmful interference' clause is pretty worthless.
"Thunderbolt, uh, does not expose PCIe lanes directly. Thunderbolt is an MPLS-like packet switching network that can encapsulate PCIe TLPs over a PHY and MAC without a spec, chips without documentation, and software with barely any support."
Additionally, the cables are twisted pair, which among other things minimizes emission. And high-speed cables are also supposed to be shielded.
I personally believe that it is real (just go camping where there's no service and you'll feel better) but it's hard to prove without decades of study and money, which won't happen because there's so much money to be made.
There are other reasons why camping makes you feel better. Earthing/grounding gets you in touch with the earth's natural schumann resonance (through the canvas tent) and the fresh air. Also too getting away from distractions.
There's a real study on this, but they don't speculate what the cause it: http://time.com/4656550/camping-sleep-insomnia/