Personally, if it were me, I would do it for awhile until you figure out a more secure long term career goal, and then go for it.
I worked at a large pet store part time through university and college (yes, I went to both - 4 year degree and one year college diploma post grad), and then for a year after while I applied for jobs in my intended feild and tried to figure out what I wanted to do.
In other words, I had a "crappy" job that did not pay well with no benefits, pension, etc etc,. don't get me wrong - I LIKED it, its just it did not offer good future prospects.
Now I have a "real" job with guarenteed 40 hours per week, good benefits, lots of advancement opportunities in the near future, and guarenteed raises as my level of certification increases. Oh, and it pays 2.5 times as much to start
What I am getting at is that, as others have mentioned, personal training might be great to do on the side, but as a career, it might be difficult to manage.
I would say do it for awhile and have fun, but while you are doing that, keep applying to other jobs that might offer more opportunities for wages, benefits and advancement.
Hope this helps.