Debilitating depression after venlafaxine increase

It's called tolerance withdrawal.  The same amount of drug no longer works and you begin to have "relapse" symptoms.  Typically doctors try to overcome it by increasing the dosage, which works for some for a period of time before they go into tolerance again.  Sometimes, though, the increase goes paradoxical.  It's like you've developed an intolerance to the drug.

It could also be that an EXCESS of serotonin is causing your symptoms by this last bump.  Everyone is told the falsehood that it is a chemical imbalance that causes depression and anxiety, but there is no evidence that a low level of serotonin is the cause of all depressions.  In fact, studies have found that 1/3 of people with depression have HIGH serotonin, 1/3 have low, and 1/3 have normal levels.  On the flip side, the same ratios occur in controls with NO depression!  So, bumping up serotonin with an SSRI/SNRI isn't always the answer to depression. It could be that you reached tolerance and are starting to have a negative response to venlafaxine.

This may sound crazy, but you can actually start to feel better by decreasing the dosage!  However, you can't just drop by 1/4 dosages even, because that can trigger withdrawal which is equally horrible if not worse. 

I was on the extended release venlafaxine with little beads in the capsules and so began reducing by removing 10% of the beads.  I have felt no worse on reducing, with the occasional bobbles if I went too fast.  The safest recommended taper rate is 10% of the previous month's dosage every 3 to 4 weeks.   I am currently down to 4.8 mg and some say that is so low you might as well stop, but I've been in the withdrawal community for three years and see horror stories about jumping off of even that much.  It is a nasty drug to come off of.  That is because our neurons remodel in the presence of the drug.  The body likes homeostasis, so when serotonin and other neurotransmitters are artificially elevated by the drugs, the body rebounds with modifications to neurons to bring levels back in line. When you come off too rapidly, you are left with those changes unopposed, and that causes the withdrawal symptoms, which can include depression and anxiety.  This is why people fail repeatedly to come off their meds; they are told that they have relapsed their original condition and need to be on the drugs!

You will be in the bind of being at the mercy of your doctor who will tell you to a) hang in there and wait for things to stabilize, b) switch you to another one, which is really bad because you will go into withdrawal from the first one and the new one won't be able to directly replace it or c) add more drugs.  Polydrugging is a real risk for psych patients because that is the medical model; medicate every symptom. Hard as it is to come off one med that doesn't work out, imagine trying to come off several!

So, I'm sorry if what I've shared is scary.  I've been there. There's a lot of support out there and if you are interested PM me and I will point you there.

So you have been on the 150 since March? That is long enough for your body to have responded to the higher dose with remodeling, so you will need to be careful about reducing.  I do think you will feel better reducing.