The issue of PCS and weights is something that I've been looking at, as it is relevant to my son's return-to-work plan (5mo. since injury), as well as his desire to maintain a fitness program, despite serious light-headedness & other symptoms.

What I have found is a fairly consistent view that lifting weights can increase intra-cranial pressure.

As for 'how heavy' is 'too heavy', I haven't found anything definitive, and this is probably an individual thing. There were a number of reports from people saying that anything above about 10lbs (or 4kg) seems to cause them problems, but I'm not whether this was in relation to repetitive weight-lifting or the occasional 'lift something and carry it'.