Weird clutch problem. Any thoughts?

Riding home tonight. All as normal until about 4 miles from home I'm thinking, clutch feels a bit spongy. Then as I shift up coming out of a left hander, clutch goes comepletely, no pressure at the lever, which won't return. Clanging and banging from gear box. Back wheel alternately free wheels and locks up.
Once stopped the bike is stuck in 2nd, clutch lever has no pressure for about half it's travel and no amount of pulling and tugging at the clutch lever/gear shifter will get it into neutral. I leave it alone for about 15 minutes, then have another go. After the 15 min break, the lever feels more 'normal' now. This time I get the bike into neutral no bother, start it up and ride home, clutch lever feels normal again.
Since getting home I have dinner go out and give it another try to see if it plays up again. It doesn't all is normal. The only thing I noticed was the clutch fluid reservoir is right down on minimum. Could this be the source of the problem and a simple top up will fix it? Anyone got any ideas?

Sounds like it needs bleeding to me at the very least. The resevoir being low is a worry, was it low before these symptoms appeared? Mine struggles to get into neutral after a proper ragging when it needs bleeding.