In 1900, his mother died.
While Thomas was at St Teilo's Hospital, mysterious time-shifts started to occur — fractures in the rift, meaning that two slices of time were superimposed and becoming confused. Torchwood Three investigated; though they could not determine at what point in the future the other slice in time existed, they recognised Tommy in one of the fractures and decided to put him in stasis and wait until the hospital entered the other side of the fracture.
Torchwood cryogenically froze Brockless; and once per year they brought him out of stasis for tests. The process gave him a unique perspective on the following century. As they had frozen his most recent memories, the shell shock was not an issue during these awakenings. In the 21st century, anomalous activity finally returned to the now-abandoned hospital and the crew of Torchwood Three sent Tommy back through the rift to 1918, so his life would be like a thread, stitching time back together again.