After pressing accidentally several keys on my keyboard I lost the Auto Completion in my PDE environment !!!
I already had the same problem long time ago but I wasn’t able to remember how I solved it. In order to solve it quickly next time and of course for others encountering it here is the solution:
Window -> Preferences -> Java -> Editor ->Content Assist Advanced -> Restore Defaults in order to have Java Proposals checked.
On a side note, I am curious to understand how I disabled this feature with my keyboard ….