“Cause of violent shaking and too weak to walk to the shower”

While a very regular exerciser (marathoner, triathelete, bicyclist etc.), my 65 year old father has had strange, uncontrollable/violent shaking for hours coupled with being too weak to walk, and a 103.5 fever with tylenol taken (this also happened again 5 days ago for 2 hours but went away). After the shaking also happened again a few days ago on 1/7/22, the next day, he went to the ER to check what he thought was another tender blood clot behind his left knee, but was a false alarm with no new blood clots (but has been on warfarin for 30 years since his last 2 PE's in the early 90's from his DVT).

He has been dealing with a lot recently, although is used to dealing with stressful situations his whole life especially as successful attorney (although recently retired), but also been grieving the loss of his close brother who died from a PE in mid-Dec. (note his dad died young over 30 years ago in Dec. from complications of diabetes), is starting a teaching job this week for BYU out of state one day a week.

He took 2 covid tests, which were clear.

Given his deadly blood clot history, should we be worried this is stemming mainly from a physical condition, or primarily from something emotional or something else perhaps?