Hello everyone.

I've recently shifted my focus to sensations in my meditation practice. Currently, I experience around four sensations per second, primarily in the torso and arms, occasionally in the legs when I intentionally focus on them. The sensations can be described as a of mice running around, pulsing and as well as ocationally snakes-like movements that feels deeper in the body. I make a note each time my mind wanders, noting intentions, as well as gross sensations like pain and tension. I have recently started to be able to notice the heat around the area of pain and tensions.

After I have finished a 45 minutes long session I find that I feel akin to waking up from a restless night's sleep. My body experiences a sense of meh, mind and body feels irritated and occasional sleepiness. I don't resist these sensations post-practice; instead, I make note of them and proceed with my day. They dissipate within 30 minutes.  I don't encounter these sensations after samatha-focused meditations (TMI).
I'm curious whether it's normal to always feel "bad" after such session or if there might be an issue with my practice.

Sure, it can be irritating, that doesn't sound strange to me. But no, it's not always like that. It usually takes a couple of months to develop a new habit like noting sensations.

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It's normal. You're doing the mind's equivalent of building new muscle. When you work out, your muscles can get sore. The symptoms of a sore mind can be a few things; irritation, boredom, and drowsiness. It'll probably just go away as you practice more.

I have noticed problems with irritability after types of meditation that involve "strong concentration" where you try to stay focused on something and make an effort not to allow distractions.

To avoid those problems I meditate "gently". It's hard to put into words how to do this - I don't make keeping focused a part of my effort. When I notice I am distracted I return to the meditation technique but there is no mental effort to stay focused during meditation, I have no thought or intention to stay focused while meditating, no mental effort not to get distracted, no mental effort blocking out distractions.

For example if I am counting my breath, and I focus intently on the counting knowing and intending that this will keep distractions away, that causes problems. If I focus on the numbers just observing them arise and fade in my mind not having any intention other than to observe I don't have problems.

It's like if it's raining out I don't use an umbrella to keep the water off, I just let the water run off by itself. Eventually the rain stops and I dry off. Eventually my mind quiets down and I have good concentration with out using force.

It is also helpful to learn to be mindful of  your mind as it chatters away. Then you don't have to worry about getting distracted while meditating, noticing the distraction is no different from any other part of whatever meditation or mindfulness practice you are doing.

I also find it helpful to keep what I call my "emotional gate" open as much as possible. This just means I try to be aware of emotions and let them flow. It doesn't mean I obsess constantly rehashing things over and over. Just, what ever arises, I don't block it. It sounds reasonable but the difficulty is that it is really easy to block things without knowing you are doing it, so it takes some attention to keep the gate open. It's hard to understand until you notice how often things can get blocked unintentionally.

This type of meditation doesn't produce problems for me:
https://ncu9nc.blogspot.com/2020/08/preparing-for-meditation-with.html

It's not uncommon for individuals to experience various emotions or sensations, including irritation, after meditation, particularly when focusing on bodily sensations. Different meditation techniques and experiences can evoke a wide range of emotional responses, and irritability is one such possibility. Here are a few reasons why you might be feeling irritated after meditating on sensations:Increased Awareness: Meditation, especially mindfulness meditation focused on bodily sensations, aims to increase awareness of the present moment. This heightened awareness may bring attention to sensations or emotions that were previously unnoticed, including those that might be uncomfortable or irritating.Unresolved Emotions: Sometimes, the practice of meditation can bring up unresolved emotions or stressors. As you become more present and aware, emotions that were previously suppressed or ignored may surface, leading to feelings of irritation. papa's freezeria

IME this is normal and it will pass.  I found it useful to do concentration practice before noting because it helped with the irritation.  You can also try a less forceful vipassana practice (slower noting, whole body noting, open awareness, noticing and so on), and this will probably cause less irritation. 

High intensity practices tend to cause some aversion in the heart, but this gets pushed away during the formal practice by strong effort.  It'll tend to come back after the sit, (or periodically during the sit where it'll get filed away as "distraction") where it might be thought of as irritation, annoyance, restlessness, or a feeling of being unsatisfied or agitated.

Sensations? 
No, not so much,
Feeling exclusively, while ignoring seeing sensations, hearing sensations, thinking sensations as somehow unworthy of investigation is different.
Perhaps you might investigate all sensations or be a bit less general when using "sensation".
Have fun body scanning
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