Well, to start with, page 202 of the PHB, under Range, says:
The target of a spell must be within the spell’s range. For
a spell like magic missile, the target is a creature. For a
spell like fireball, the target is the point in space where
the ball of fire erupts.
So there's that. Then on the next page, under Targets, we have:
To target something, you must have a clear path to it,
so it can’t be behind total cover.
If you place an area of effect at a point that you can’t
see and an obstruction, such as a wall, is between you
and that point, the point of origin comes into being on the
near side of that obstruction.
This is interesting, because it clearly indicates that it is possible to target area of effect spells on locations that you can't see. If it hits something on the way, the area of effect will be created there, but otherwise, go nuts.
This is all that the rules say about targeting AoE spells. It's up to you and your DM to decide, in a specific situation, whether you would be able to target a specific point.
Yes, this should work
There is no language in the spell that requires you to "see" your target location, just that you pick a point within 120' of you.
In addition, you know exactly where you are, so you could choose to go "blind" and cast the spell.
Caveat Emptor
You may now be under the Blinded condition until the start of your next turn. Whether or not your DM will allow you to re-open your eyes will likely be under their control. Hypnotic Pattern "appears for a moment" so you may be able to reopen, but it would also be very understandable that you need to have your eyes closed for your turn in order to avoid the effects. This would put you under the Blinded condition until the start of your next turn.
Best Answer
Per the spell description, the target(s) must be able to see the patterns created by the spell. Since the spell creates swirling patterns of color, I would rule that even in complete darkness the target(s) can see it, unless their eyes are closed or otherwise obscured.
My reasoning for this is that swirling patterns of color, on their own, as a magical effect, must be light-based. Though they don't emit light in the sense that a torch does, they must be visible. The spell components here are either a glowing stick of incense or a crystal vial filled with phosphorescent material -- essentially a sparkler or a glowstick. The effect that most people are probably familiar with is that of a glowstick or sparkler leaving trails across your vision in the dark. One might even say these trails create hypnotic patterns.