Begin by standing tall in Mountain Pose (Tadasana) with your weight equally distributed in both feet. Shift your weight onto the right foot. Bend your left knee to lift your left foot off the floor. Keep your left knee hugging toward your midline throughout this pose.

#1 Pain and/or numbness are signals from your body, saying it's over extended and it is going to check out until conditions improve. I experienced something similar in shoulderstand for a long time. At that time I was using a strap to pull my arms to a specific position. I don't do it that way anymore, and get the same benefits from the pose.

You also said in comments that you feel a numbness in Trikonasana or Triangle pose...and that you think it's part of the pose, but
I have been practicing for 7 years, and have never experienced any numbness from Trikonasana. I also haven't heard any of my teachers describe numbness as a part of any pose (and I've been lucky enough to study with some top teachers), except the shoulderstand one...and other teachers have refuted that.

For Triangle- I ask students to put the top arm on their hips to focus the pose on the lower body. Trikonasana/Triangle is a wonderful pose to strengthen the legs.

My "upshot"...
If you are experiencing numbness use this as feedback. Play with the poses at home, if you have difficulty exploring them in class.

Natarajasana (Dancer Pose or Lord of the Dance Pose) is a deep backbend that requires patience, focus, and persistence. The pose is named after the Hindu god Shiva Nataraja, King of the Dance, who finds bliss in the midst of destruction. Like its namesake, Lord of the Dance Pose embodies finding steadying calm within.

https://www.easyflexibility.com/blogs/flexibility-pearls/if-can-do-one-type-of-split-should-i-be-able-to-do-another-one-automatically-part-4