BE36 pilot reported a temporary loss of control during approach. The pilot corrected altitude and heading deviations and completed a safe landing.

Narrative

On Day 0 I departed ZZZ1 in Aircraft X at XA38; destined for ZZZ. The pre-flight weather briefing generally indicated a broken layer at 1;200 AGL at ZZZ1 with clear skies at ZZZ2 and clearing skies at ZZZ3 indicating the typical coastal marine layer was burning off. My typical flight plan for this flight is ZZZ1 direct to ZZZ2 then fly the LOC Runway XX approach to ZZZ. I make this flight 20+ times per year. During the leg from ZZZ1 to ZZZ; I noticed my Autopilot was intermittently wandering in altitude and heading; so I hand flew most of the way.When I began to approach the ZZZ airspace; I noticed the marine layer had not yet significantly burned off toward the coast and ZZZ ATIS was indicating 1;200 overcast. I radioed ZZZ Approach and requested an IFR clearance into ZZZ. The controller instructed me to fly direct to ZZZ4 and hold. At this point since the aircraft Autopilot was unreliable; I decided to hand fly the arrival procedure and approach. Next he cleared me to ZZZ via the ZZZ4 270 radial to intercept the localizer and fly the VOR approach. I joined the localizer at altitude 3;000 MSL and began to fly over the tops which were at roughly 2;800 MSL. Next; while flying the localizer course; I received a new Approach frequency and the new controller cleared me down to 2;600 MSL. I descended into the IMC and held as instructed at 2;600 momentarily. Next; I noticed that my VSI was trending downward and my HSI was indicating a right turn. I quickly attempted to correct the situation by pulling up and turning left but the VSI quickly dropped to negative 1;000 FPM descent. At that time; the controller radioed me with an altitude alert stating that I was descending at 1;000 FPM. As I continued to attempt to overcome the bank and descent; fighting against my perceived orientation; I became aware that I was experiencing special disorientation. Fortunately at about that point; I broke out below the cloud layer and was quickly able to; level the wings and stop the descent at roughly 1;800 MSL. I informed the controller I had experienced disorientation and was now okay. She advised me to turn back to the localizer course; intercept it and climb back to 2;600 MSL which I did. As I reintercepted the localizer I began to climb back into IMC at around 2;000 MSL but was again having difficulty manually holding the localizer course; again trending to the right (north). So I descended back beneath the clouds. At this point; the controller told me she was [requesting priority handling] for me and offered me the option to land at ZZZ5; approximately 5 miles to the south. I told her I preferred to continue to ZZZ as that is my most familiar airport. After a brief time on the localizer at +/- 1;800 MSL; I advised her I had the ZZZ field in sight. She told me to contact the Tower which I did and landed at ZZZ without incident. HUMAN PERFORMANCE CONSIDERATIONS Perceptions; judgements; decisions:My perception/judgment was that my skills were sufficient that I would be able to hand fly the approach through the IMC. This led to a bad decision to proceed with the IMC approach with a disabled Autopilot.- Factors affecting the quality of human performance:Perhaps too much time had elapsed since my last practice approach session with my instructor in simulated IMC. I generally try to do this a couple times per year although the COVID pandemic interfered with this routine. I did my BFR/IPC with him in 2 months prior.- Actions or inactions.A better course of action would have been for me to land the aircraft at a nearby airport with VFR conditions as my Autopilot was effectively inoperable for the approach.What can be done to prevent a recurrence; or correct the situation: I have will take several corrective actions to prevent this from happening again:1. The aircraft will be receiving an entirely new avionics system including Garmin flat screen panels; new auto pilot; GPS; Nav/Com. All the existing avionics gear will be replaced. The upgrade is being performed by Company and is scheduled to commence in one month. The upgrade will take +/- 8 weeks to perform as it is a complete rebuild of the panel and all the systems. The new avionics will be more reliable and easier to operate; significantly reducing the likelihood of spatial disorientation.2. I will attempt to complete an IPC with my instructor ASAP using the existing avionics systems to help me understand where I might have failed or how I became disoriented. 3. After the new avionics systems are installed; I will undergo extensive training both on line and with my instructor in the aircraft until I feel comfortable enough with the systems to fly.4. I will not fly IFR/IMC or marginal VFR until after my new avionics system is installed and I am fully trained; checked out and have completed an IPC using the new systems.