I've just finished my nav's and felt stressed to the point of giving up all the way through until the solo nav, where all that practice I had been absorbing somehow kicked in and it was a breeze, I've never had such an enjoyable flight. Hang in there!
I found that less is more - I didn't use the whizz wheel in flight, or the tables I used for initial planning. I mentally worked things out if I had to. I also wrote it all on pages of the map I had photocopied, so I had one set of papers to deal with only. I used a cheap digital watch, with a BIG display, which helped a lot, and wrote the numbers on the map.
Get the basics in place, get used to what terrain looks like, how clouds sit on mountains, how small a rail line is from the air etc. then progress to using navigation tools in the air. Simply things and build it up lesson by lesson, don't go all out from the start.
I also learned not to look at the map. You have to have faith in your ability to pick a point ahead and fly to it, and not try match map to ground all the time, as it stresses you, or it did me anyway. I found by not looking at the map except where I expected to be near my next feature, it calmed me down which allowed me to think more and not panick and get lost.
And think about your definition of lost. I'm near the sea here so I know if I'm in trouble, fly East, avoid some controlled airspace and I will find the sea and then find my way home. I can't get lost if I think of it in that simplistic manner, hence I don't stress about it.
Also remember it's not a simple add on like doing the radio endoresement, it's a major achievement and hence will take quite a bit of time and effort and stress, I found it a lot more so than doing the initial training. If you accept the size of what you are doing, you may find it okay.
Good luck.
Ryan