It can be terrifying when you can feel yourself going downhill - I always say it feels like when you're so tired you feel like you're heavy. I hear you, and I'm so sorry you're feeling this way at the moment.
It sounds like you're doing the right things - obviously, you can't fake it til you make it with mental illness, but there are things that will help you maintain some grip on normality, and making sure you get up, eat, shower if you can, is way better than just detatching from life at all. That is your will to keep a handle on things showing and that's a really good sign.
4 weeks on venlafexine means it's getting into your system now and in the next couple of weeks you should start feeling some relief. Keep trying the crisis team - again, a good sign that you have the will to keep going and try to get help.
You probably feel like you have no control right now, like you're at the whim of your brain chemistry, and overwhelmed. What's clear from reading your post is that while the feelings are a very overwhelming and scary thing to face, you are grounding yourself so well. You are maintaining connections by talking to your partner, you are continuing to eat and get up and refuse to be detatched from daily life. You are taking your medication, contacting people for help: you may not feel like it, but you are advocating for yourself and your health as best you can at the moment. You're obviously very self aware and able to recognise shifts in your mental state and that's a good sign, too - it means you're able to identify what's happening to you and identify that the way you feel is a 'state' not a permanent thing. That's no small thing and it's better than I've done in the past. You're doing so, so well - as someone who knows exactly how you feel, I'm proud of you.
For tonight and the next few days: don't be afraid to lean on your partner and the people around you, to ask them for what you need. Sometimes you give 50/50 in any relationship and sometimes it's 90/10, or 100/0. Tell them if you need to put a film on and sit in silence and just hold their hand, tell them if you need to just vent for 10 minutes about how horrendous everything feels and you don't need them to say anything, tell them if you need a friend to come and drive you around for 20 minutes while you have a cry but not alone.
And I'll keep an eye on this thread, if you want to get your thoughts out to some strangers on the internet. 