Snowkitten, I'm really sorry that you're going through this. When I was still with my (then) DP, I thought the problems stemmed from depression or anxiety. And maybe they do. But the biggest, and most immediate issue by far was the drinking. My (then)DP is extremely volatile when she's been drinking heavily for a while - she can flip from laughing and joking to snarling aggression in, literally, a couple of seconds and for no obvious reason. But she always, always blames those around her for her mood swings even when it's plainly obvious that it's just because she's pissed and aggressive.
The other thing to consider is that daily heavy drinking has a cumulative effect. If your DH is drinking anywhere near as much as you suspect he is (and I'd agree the chances are he's drinking in secret as well as the stuff you're seeing) then he's likely not sobering up properly before he's drinking again. The jittery stuff you've been seeing could very well be Alcohol Withdrawal Symptoms.
If your DH does have depression then it is untreatable until and unless he stops drinking. From your point of view, I'd suggest you look at this as an alcohol issue first and foremost and if (and it's sad to say but that's a very a big "if") he deals with that, to then look at what, if any, problems remain.
This is a crappy time of year for you to be dealing with this. Sadly, Christmas is often a time when families of those with alcohol problems really bear the full brunt of those problems. If you haven't already, do confide in a few friends and family that you trust. It will help.
Try to avoid any serious conversations with him when he's been drinking as it will get you nowhere and merely raise your stress levels. You won't get anything resolved by talking to a drunk person. "I'm sorry, but I really don't wish to discuss this now" said as calmly as possible can help. Leaving the room, putting the phone down, they can also help remove yourself from the immediate issue. But don't hesitate to call the police if need be. Your safety, and the safety of your children, is paramount.