3 yr old with stroke like symptons

2 1/2 years my 4 year old started having swelling to the back of the head which lasted for about 5 days then went down, this then came back a few weeks later. This lasted for over 2 years with bleeding between the skull and skin which went to the side of the head then to the side of the face. MRI/CT showed normal, possibly lymphigioma but didn't act like it does. a biopsy was done and found a lump on skull and a burst cyst. Docs are stuck to answer this. Anyway 2 months ago my son had a 'seizure (episode) where his speech went slurred, legs became wobbly so couldn't stand without falling over,couldn't sit up all symptons of mennigitus or a stroke. After 8 hours he was fine. THis has happened 5 times since, each recovering within 8 hours, only once loosing consiousnous. CT/Mri, EEG, blood tests all normal, docs are stuck to answer this, been seen by uk leading poedatricions, but they don't know. Any idea, he also can't remember these happening.